Merge branch 'master' into lm_warnings

7 files changed, 900 insertions, 266 deletions

diff --git a/src/libslic3r/SLA/SLABasePool.cpp b/src/libslic3r/SLA/SLABasePool.cpp
index 3b199c4eb..4ce84ba02 100644
--- a/src/libslic3r/SLA/SLABasePool.cpp
+++ b/src/libslic3r/SLA/SLABasePool.cpp
@@ -5,11 +5,12 @@
 #include "SLABoostAdapter.hpp"
 #include "ClipperUtils.hpp"
 #include "Tesselate.hpp"
+#include "MTUtils.hpp"
 
 // For debugging:
-//#include <fstream>
-//#include <libnest2d/tools/benchmark.h>
-//#include "SVG.hpp"
+// #include <fstream>
+// #include <libnest2d/tools/benchmark.h>
+// #include "SVG.hpp"
 
 namespace Slic3r { namespace sla {
 
@@ -183,9 +184,10 @@ Contour3D walls(const Polygon& lower, const Polygon& upper,
 }
 
 /// Offsetting with clipper and smoothing the edges into a curvature.
-void offset(ExPolygon& sh, coord_t distance) {
+void offset(ExPolygon& sh, coord_t distance, bool edgerounding = true) {
     using ClipperLib::ClipperOffset;
     using ClipperLib::jtRound;
+    using ClipperLib::jtMiter;
     using ClipperLib::etClosedPolygon;
     using ClipperLib::Paths;
     using ClipperLib::Path;
@@ -202,11 +204,13 @@ void offset(ExPolygon& sh, coord_t distance) {
         return;
     }
 
+    auto jointype = edgerounding? jtRound : jtMiter;
+    
     ClipperOffset offs;
-    offs.ArcTolerance = 0.01*scaled(1.0);
+    offs.ArcTolerance = scaled<double>(0.01);
     Paths result;
-    offs.AddPath(ctour, jtRound, etClosedPolygon);
-    offs.AddPaths(holes, jtRound, etClosedPolygon);
+    offs.AddPath(ctour, jointype, etClosedPolygon);
+    offs.AddPaths(holes, jointype, etClosedPolygon);
     offs.Execute(result, static_cast<double>(distance));
 
     // Offsetting reverts the orientation and also removes the last vertex
@@ -236,6 +240,50 @@ void offset(ExPolygon& sh, coord_t distance) {
     }
 }
 
+void offset(Polygon &sh, coord_t distance, bool edgerounding = true)
+{
+    using ClipperLib::ClipperOffset;
+    using ClipperLib::jtRound;
+    using ClipperLib::jtMiter;
+    using ClipperLib::etClosedPolygon;
+    using ClipperLib::Paths;
+    using ClipperLib::Path;
+
+    auto &&ctour = Slic3rMultiPoint_to_ClipperPath(sh);
+
+    // If the input is not at least a triangle, we can not do this algorithm
+    if (ctour.size() < 3) {
+        BOOST_LOG_TRIVIAL(error) << "Invalid geometry for offsetting!";
+        return;
+    }
+
+    ClipperOffset offs;
+    offs.ArcTolerance = 0.01 * scaled(1.);
+    Paths result;
+    offs.AddPath(ctour, edgerounding ? jtRound : jtMiter, etClosedPolygon);
+    offs.Execute(result, static_cast<double>(distance));
+
+    // Offsetting reverts the orientation and also removes the last vertex
+    // so boost will not have a closed polygon.
+
+    bool found_the_contour = false;
+    for (auto &r : result) {
+        if (ClipperLib::Orientation(r)) {
+            // We don't like if the offsetting generates more than one contour
+            // but throwing would be an overkill. Instead, we should warn the
+            // caller about the inability to create correct geometries
+            if (!found_the_contour) {
+                auto rr = ClipperPath_to_Slic3rPolygon(r);
+                sh.points.swap(rr.points);
+                found_the_contour = true;
+            } else {
+                BOOST_LOG_TRIVIAL(warning)
+                    << "Warning: offsetting result is invalid!";
+            }
+        }
+    }
+}
+
 /// Unification of polygons (with clipper) preserving holes as well.
 ExPolygons unify(const ExPolygons& shapes) {
     using ClipperLib::ptSubject;
@@ -306,6 +354,116 @@ ExPolygons unify(const ExPolygons& shapes) {
     return retv;
 }
 
+Polygons unify(const Polygons& shapes) {
+    using ClipperLib::ptSubject;
+    
+    bool closed = true;
+    bool valid = true;
+
+    ClipperLib::Clipper clipper;
+
+    for(auto& path : shapes) {
+        auto clipperpath = Slic3rMultiPoint_to_ClipperPath(path);
+
+        if(!clipperpath.empty())
+            valid &= clipper.AddPath(clipperpath, ptSubject, closed);
+    }
+
+    if(!valid) BOOST_LOG_TRIVIAL(warning) << "Unification of invalid shapes!";
+
+    ClipperLib::Paths result;
+    clipper.Execute(ClipperLib::ctUnion, result, ClipperLib::pftNonZero);
+
+    Polygons ret;
+    for (ClipperLib::Path &p : result) {
+        Polygon pp = ClipperPath_to_Slic3rPolygon(p);
+        if (!pp.is_clockwise()) ret.emplace_back(std::move(pp));
+    }
+    
+    return ret;
+}
+
+// Function to cut tiny connector cavities for a given polygon. The input poly
+// will be offsetted by "padding" and small rectangle shaped cavities will be
+// inserted along the perimeter in every "stride" distance. The stick rectangles
+// will have a with about "stick_width". The input dimensions are in world 
+// measure, not the scaled clipper units.
+void breakstick_holes(ExPolygon& poly,
+                      double padding,
+                      double stride,
+                      double stick_width,
+                      double penetration)
+{   
+    // SVG svg("bridgestick_plate.svg");
+    // svg.draw(poly);
+
+    auto transf = [stick_width, penetration, padding, stride](Points &pts) {
+        // The connector stick will be a small rectangle with dimensions
+        // stick_width x (penetration + padding) to have some penetration
+        // into the input polygon.
+
+        Points out;
+        out.reserve(2 * pts.size()); // output polygon points
+
+        // stick bottom and right edge dimensions
+        double sbottom = scaled(stick_width);
+        double sright  = scaled(penetration + padding);
+
+        // scaled stride distance
+        double sstride = scaled(stride);
+        double t       = 0;
+
+        // process pairs of vertices as an edge, start with the last and
+        // first point
+        for (size_t i = pts.size() - 1, j = 0; j < pts.size(); i = j, ++j) {
+            // Get vertices and the direction vectors
+            const Point &a = pts[i], &b = pts[j];
+            Vec2d        dir = b.cast<double>() - a.cast<double>();
+            double       nrm = dir.norm();
+            dir /= nrm;
+            Vec2d dirp(-dir(Y), dir(X));
+
+            // Insert start point
+            out.emplace_back(a);
+
+            // dodge the start point, do not make sticks on the joins
+            while (t < sbottom) t += sbottom;
+            double tend = nrm - sbottom;
+
+            while (t < tend) { // insert the stick on the polygon perimeter
+
+                // calculate the stick rectangle vertices and insert them
+                // into the output.
+                Point p1 = a + (t * dir).cast<coord_t>();
+                Point p2 = p1 + (sright * dirp).cast<coord_t>();
+                Point p3 = p2 + (sbottom * dir).cast<coord_t>();
+                Point p4 = p3 + (sright * -dirp).cast<coord_t>();
+                out.insert(out.end(), {p1, p2, p3, p4});
+
+                // continue along the perimeter
+                t += sstride;
+            }
+
+            t = t - nrm;
+
+            // Insert edge endpoint
+            out.emplace_back(b);
+        }
+        
+        // move the new points
+        out.shrink_to_fit();
+        pts.swap(out);
+    };
+    
+    if(stride > 0.0 && stick_width > 0.0 && padding > 0.0) {
+        transf(poly.contour.points);
+        for (auto &h : poly.holes) transf(h.points);
+    }
+    
+    // svg.draw(poly);
+    // svg.Close();
+}
+
 /// This method will create a rounded edge around a flat polygon in 3d space.
 /// 'base_plate' parameter is the target plate.
 /// 'radius' is the radius of the edges.
@@ -351,7 +509,7 @@ Contour3D round_edges(const ExPolygon& base_plate,
         double x2 = xx*xx;
         double stepy = std::sqrt(r2 - x2);
 
-        offset(ob, s*scaled(xx));
+        offset(ob, s * scaled(xx));
         wh = ceilheight_mm - radius_mm + stepy;
 
         Contour3D pwalls;
@@ -375,7 +533,7 @@ Contour3D round_edges(const ExPolygon& base_plate,
             double xx = radius_mm - i*stepx;
             double x2 = xx*xx;
             double stepy = std::sqrt(r2 - x2);
-            offset(ob, s*scaled(xx));
+            offset(ob, s * scaled(xx));
             wh = ceilheight_mm - radius_mm - stepy;
 
             Contour3D pwalls;
@@ -425,41 +583,38 @@ inline Point centroid(Points& pp) {
     return c;
 }
 
-inline Point centroid(const ExPolygon& poly) {
-    return poly.contour.centroid();
+inline Point centroid(const Polygon& poly) {
+    return poly.centroid();
 }
 
 /// A fake concave hull that is constructed by connecting separate shapes
 /// with explicit bridges. Bridges are generated from each shape's centroid
 /// to the center of the "scene" which is the centroid calculated from the shape
 /// centroids (a star is created...)
-ExPolygons concave_hull(const ExPolygons& polys, double max_dist_mm = 50,
-                        ThrowOnCancel throw_on_cancel = [](){})
+Polygons concave_hull(const Polygons& polys, double max_dist_mm = 50,
+                      ThrowOnCancel throw_on_cancel = [](){})
 {
     namespace bgi = boost::geometry::index;
-    using SpatElement = std::pair<BoundingBox, unsigned>;
+    using SpatElement = std::pair<Point, unsigned>;
     using SpatIndex = bgi::rtree< SpatElement, bgi::rstar<16, 4> >;
 
-    if(polys.empty()) return ExPolygons();
+    if(polys.empty()) return Polygons();
+    
+    const double max_dist = scaled(max_dist_mm);
 
-    ExPolygons punion = unify(polys);   // could be redundant
+    Polygons punion = unify(polys);   // could be redundant
 
     if(punion.size() == 1) return punion;
 
     // We get the centroids of all the islands in the 2D slice
     Points centroids; centroids.reserve(punion.size());
     std::transform(punion.begin(), punion.end(), std::back_inserter(centroids),
-                   [](const ExPolygon& poly) { return centroid(poly); });
-
-
-    SpatIndex boxindex; unsigned idx = 0;
-    std::for_each(punion.begin(), punion.end(),
-                  [&boxindex, &idx](const ExPolygon& expo) {
-        BoundingBox bb(expo);
-        boxindex.insert(std::make_pair(bb, idx++));
-    });
-
+                   [](const Polygon& poly) { return centroid(poly); });
 
+    SpatIndex ctrindex;
+    unsigned  idx = 0;
+    for(const Point &ct : centroids) ctrindex.insert(std::make_pair(ct, idx++));
+    
     // Centroid of the centroids of islands. This is where the additional
     // connector sticks are routed.
     Point cc = centroid(centroids);
@@ -469,30 +624,37 @@ ExPolygons concave_hull(const ExPolygons& polys, double max_dist_mm = 50,
     idx = 0;
     std::transform(centroids.begin(), centroids.end(),
                    std::back_inserter(punion),
-                   [&punion, &boxindex, cc, max_dist_mm, &idx, throw_on_cancel]
+                   [&centroids, &ctrindex, cc, max_dist, &idx, throw_on_cancel]
                    (const Point& c)
     {
         throw_on_cancel();
         double dx = x(c) - x(cc), dy = y(c) - y(cc);
         double l = std::sqrt(dx * dx + dy * dy);
         double nx = dx / l, ny = dy / l;
-        double max_dist = scaled(max_dist_mm);
-
-        ExPolygon& expo = punion[idx++];
-        BoundingBox querybb(expo);
-
-        querybb.offset(max_dist);
+        
+        Point& ct = centroids[idx];
+        
         std::vector<SpatElement> result;
-        boxindex.query(bgi::intersects(querybb), std::back_inserter(result));
-        if(result.size() <= 1) return ExPolygon();
+        ctrindex.query(bgi::nearest(ct, 2), std::back_inserter(result));
 
-        ExPolygon r;
-        auto& ctour = r.contour.points;
+        double dist = max_dist;
+        for (const SpatElement &el : result)
+            if (el.second != idx) {
+                dist = Line(el.first, ct).length();
+                break;
+            }
+        
+        idx++;
+        
+        if (dist >= max_dist) return Polygon();
+        
+        Polygon r;
+        auto& ctour = r.points;
 
         ctour.reserve(3);
         ctour.emplace_back(cc);
 
-        Point d(coord_t(scaled(1.)*nx), coord_t(scaled(1.)*ny));
+        Point d(scaled(nx), scaled(ny));
         ctour.emplace_back(c + Point( -y(d),  x(d) ));
         ctour.emplace_back(c + Point(  y(d), -x(d) ));
         offset(r, scaled(1.));
@@ -506,42 +668,55 @@ ExPolygons concave_hull(const ExPolygons& polys, double max_dist_mm = 50,
     return punion;
 }
 
-void base_plate(const TriangleMesh &mesh, ExPolygons &output, float h,
-                float layerh, ThrowOnCancel thrfn)
+void base_plate(const TriangleMesh &      mesh,
+                ExPolygons &              output,
+                const std::vector<float> &heights,
+                ThrowOnCancel             thrfn)
 {
-    TriangleMesh m = mesh;
-    m.require_shared_vertices(); // TriangleMeshSlicer needs this
-    TriangleMeshSlicer slicer(&m);
-
-    auto bb = mesh.bounding_box();
-    float gnd = float(bb.min(Z));
-    std::vector<float> heights = {float(bb.min(Z))};
-    for(float hi = gnd + layerh; hi <= gnd + h; hi += layerh)
-        heights.emplace_back(hi);
-
-    std::vector<ExPolygons> out; out.reserve(size_t(std::ceil(h/layerh)));
+    if (mesh.empty()) return;
+    //    m.require_shared_vertices(); // TriangleMeshSlicer needs this    
+    TriangleMeshSlicer slicer(&mesh);
+    
+    std::vector<ExPolygons> out; out.reserve(heights.size());
     slicer.slice(heights, 0.f, &out, thrfn);
-
+    
     size_t count = 0; for(auto& o : out) count += o.size();
-
+    
     // Now we have to unify all slice layers which can be an expensive operation
     // so we will try to simplify the polygons
     ExPolygons tmp; tmp.reserve(count);
     for(ExPolygons& o : out)
         for(ExPolygon& e : o) {
-            auto&& exss = e.simplify(scaled(0.1));
+            auto&& exss = e.simplify(scaled<double>(0.1));
             for(ExPolygon& ep : exss) tmp.emplace_back(std::move(ep));
         }
-
+    
     ExPolygons utmp = unify(tmp);
-
+    
     for(auto& o : utmp) {
-        auto&& smp = o.simplify(scaled(0.1));
+        auto&& smp = o.simplify(scaled<double>(0.1));
         output.insert(output.end(), smp.begin(), smp.end());
     }
 }
 
-Contour3D create_base_pool(const ExPolygons &ground_layer, 
+void base_plate(const TriangleMesh &mesh,
+                ExPolygons &        output,
+                float               h,
+                float               layerh,
+                ThrowOnCancel       thrfn)
+{
+    auto bb = mesh.bounding_box();
+    float gnd = float(bb.min(Z));
+    std::vector<float> heights = {float(bb.min(Z))};
+    
+    for(float hi = gnd + layerh; hi <= gnd + h; hi += layerh)
+        heights.emplace_back(hi);
+    
+    base_plate(mesh, output, heights, thrfn);
+}
+
+Contour3D create_base_pool(const Polygons &ground_layer, 
+                           const ExPolygons &obj_self_pad = {},
                            const PoolConfig& cfg = PoolConfig()) 
 {
     // for debugging:
@@ -556,7 +731,7 @@ Contour3D create_base_pool(const ExPolygons &ground_layer,
     // serve as the bottom plate of the pad. We will offset this concave hull
     // and then offset back the result with clipper with rounding edges ON. This
     // trick will create a nice rounded pad shape.
-    ExPolygons concavehs = concave_hull(ground_layer, mergedist, cfg.throw_on_cancel);
+    Polygons concavehs = concave_hull(ground_layer, mergedist, cfg.throw_on_cancel);
 
     const double thickness      = cfg.min_wall_thickness_mm;
     const double wingheight     = cfg.min_wall_height_mm;
@@ -576,42 +751,37 @@ Contour3D create_base_pool(const ExPolygons &ground_layer,
 
     Contour3D pool;
 
-    for(ExPolygon& concaveh : concavehs) {
-        if(concaveh.contour.points.empty()) return pool;
-
-        // Get rid of any holes in the concave hull output.
-        concaveh.holes.clear();
+    for(Polygon& concaveh : concavehs) {
+        if(concaveh.points.empty()) return pool;
 
         // Here lies the trick that does the smoothing only with clipper offset
         // calls. The offset is configured to round edges. Inner edges will
         // be rounded because we offset twice: ones to get the outer (top) plate
         // and again to get the inner (bottom) plate
         auto outer_base = concaveh;
-        outer_base.holes.clear();
         offset(outer_base, s_safety_dist + s_wingdist + s_thickness);
 
-        ExPolygon bottom_poly = outer_base;
-        bottom_poly.holes.clear();
+        ExPolygon bottom_poly; bottom_poly.contour = outer_base;
         offset(bottom_poly, -s_bottom_offs);
 
         // Punching a hole in the top plate for the cavity
         ExPolygon top_poly;
         ExPolygon middle_base;
         ExPolygon inner_base;
-        top_poly.contour = outer_base.contour;
+        top_poly.contour = outer_base;
 
         if(wingheight > 0) {
-            inner_base = outer_base;
+            inner_base.contour = outer_base;
             offset(inner_base, -(s_thickness + s_wingdist + s_eradius));
 
-            middle_base = outer_base;
+            middle_base.contour = outer_base;
             offset(middle_base, -s_thickness);
             top_poly.holes.emplace_back(middle_base.contour);
             auto& tph = top_poly.holes.back().points;
             std::reverse(tph.begin(), tph.end());
         }
 
-        ExPolygon ob = outer_base; double wh = 0;
+        ExPolygon ob; ob.contour = outer_base; double wh = 0;
 
         // now we will calculate the angle or portion of the circle from
         // pi/2 that will connect perfectly with the bottom plate.
@@ -658,6 +828,7 @@ Contour3D create_base_pool(const ExPolygons &ground_layer,
         if(wingheight > 0) {
             // Generate the smoothed edge geometry
             wh = 0;
+            ob = middle_base;
             if(s_eradius) pool.merge(round_edges(middle_base,
                                    r,
                                    phi - 90, // from tangent lines
@@ -672,11 +843,59 @@ Contour3D create_base_pool(const ExPolygons &ground_layer,
                              wh, -wingdist, thrcl));
         }
 
-        // Now we need to triangulate the top and bottom plates as well as the
-        // cavity bottom plate which is the same as the bottom plate but it is
-        // elevated by the thickness.
+        if (cfg.embed_object) {
+            ExPolygons bttms = diff_ex(to_polygons(bottom_poly),
+                                       to_polygons(obj_self_pad));
+            
+            assert(!bttms.empty());
+            
+            std::sort(bttms.begin(), bttms.end(),
+                      [](const ExPolygon& e1, const ExPolygon& e2) {
+                          return e1.contour.area() > e2.contour.area();
+                      });
+            
+            if(wingheight > 0) inner_base.holes = bttms.front().holes;
+            else top_poly.holes = bttms.front().holes;
+
+            auto straight_walls =
+                [&pool](const Polygon &cntr, coord_t z_low, coord_t z_high) {
+                    
+                auto lines = cntr.lines();
+                
+                for (auto &l : lines) {
+                    auto s = coord_t(pool.points.size());
+                    auto& pts = pool.points;
+                    pts.emplace_back(unscale(l.a.x(), l.a.y(), z_low));
+                    pts.emplace_back(unscale(l.b.x(), l.b.y(), z_low));
+                    pts.emplace_back(unscale(l.a.x(), l.a.y(), z_high));
+                    pts.emplace_back(unscale(l.b.x(), l.b.y(), z_high));
+                    
+                    pool.indices.emplace_back(s, s + 1, s + 3);
+                    pool.indices.emplace_back(s, s + 3, s + 2);
+                }
+            };
+            
+            coord_t z_lo = -scaled(fullheight), z_hi = -scaled(wingheight);
+            for (ExPolygon &ep : bttms) {
+                pool.merge(triangulate_expolygon_3d(ep, -fullheight, true));
+                for (auto &h : ep.holes) straight_walls(h, z_lo, z_hi);
+            }
+            
+            // Skip the outer contour, triangulate the holes
+            for (auto it = std::next(bttms.begin()); it != bttms.end(); ++it) {
+                pool.merge(triangulate_expolygon_3d(*it, -wingheight));
+                straight_walls(it->contour, z_lo, z_hi);
+            }
+            
+        } else {
+            // Now we need to triangulate the top and bottom plates as well as
+            // the cavity bottom plate which is the same as the bottom plate
+            // but it is elevated by the thickness.
+            
+            pool.merge(triangulate_expolygon_3d(bottom_poly, -fullheight, true));
+        }
+        
         pool.merge(triangulate_expolygon_3d(top_poly));
-        pool.merge(triangulate_expolygon_3d(bottom_poly, -fullheight, true));
 
         if(wingheight > 0)
             pool.merge(triangulate_expolygon_3d(inner_base, -wingheight));
@@ -686,8 +905,8 @@ Contour3D create_base_pool(const ExPolygons &ground_layer,
     return pool;
 }
 
-void create_base_pool(const ExPolygons &ground_layer, TriangleMesh& out,
-                      const PoolConfig& cfg)
+void create_base_pool(const Polygons &ground_layer, TriangleMesh& out,
+                      const ExPolygons &holes, const PoolConfig& cfg)
 {
     
 
@@ -697,7 +916,7 @@ void create_base_pool(const ExPolygons &ground_layer, TriangleMesh& out,
     // std::fstream fout("pad_debug.obj", std::fstream::out);
     // if(fout.good()) pool.to_obj(fout);
 
-    out.merge(mesh(create_base_pool(ground_layer, cfg)));
+    out.merge(mesh(create_base_pool(ground_layer, holes, cfg)));
 }
 
 }
diff --git a/src/libslic3r/SLA/SLABasePool.hpp b/src/libslic3r/SLA/SLABasePool.hpp
index 3c88e58c8..67b9ccdcb 100644
--- a/src/libslic3r/SLA/SLABasePool.hpp
+++ b/src/libslic3r/SLA/SLABasePool.hpp
@@ -8,7 +8,9 @@
 namespace Slic3r {
 
 class ExPolygon;
+class Polygon;
 using ExPolygons = std::vector<ExPolygon>;
+using Polygons = std::vector<Polygon>;
 
 class TriangleMesh;
 
@@ -19,16 +21,40 @@ using ThrowOnCancel = std::function<void(void)>;
 /// Calculate the polygon representing the silhouette from the specified height
 void base_plate(const TriangleMesh& mesh,       // input mesh
                 ExPolygons& output,             // Output will be merged with
-                float zlevel = 0.1f,            // Plate creation level
+                float samplingheight = 0.1f,    // The height range to sample
                 float layerheight = 0.05f,      // The sampling height
                 ThrowOnCancel thrfn = [](){});  // Will be called frequently
 
+void base_plate(const TriangleMesh& mesh,       // input mesh
+                ExPolygons& output,             // Output will be merged with
+                const std::vector<float>&,      // Exact Z levels to sample
+                ThrowOnCancel thrfn = [](){});  // Will be called frequently
+
+// Function to cut tiny connector cavities for a given polygon. The input poly
+// will be offsetted by "padding" and small rectangle shaped cavities will be
+// inserted along the perimeter in every "stride" distance. The stick rectangles
+// will have a with about "stick_width". The input dimensions are in world 
+// measure, not the scaled clipper units.
+void breakstick_holes(ExPolygon &poly,
+                      double     padding,
+                      double     stride,
+                      double     stick_width,
+                      double     penetration = 0.0);
+
 struct PoolConfig {
     double min_wall_thickness_mm = 2;
     double min_wall_height_mm = 5;
     double max_merge_distance_mm = 50;
     double edge_radius_mm = 1;
     double wall_slope = std::atan(1.0);          // Universal constant for Pi/4
+    struct EmbedObject {
+        double object_gap_mm = 0.5;
+        double stick_stride_mm = 10;
+        double stick_width_mm = 0.3;
+        double stick_penetration_mm = 0.1;
+        bool enabled = false;
+        operator bool() const { return enabled; }
+    } embed_object;
 
     ThrowOnCancel throw_on_cancel = [](){};
 
@@ -42,15 +68,12 @@ struct PoolConfig {
 };
 
 /// Calculate the pool for the mesh for SLA printing
-void create_base_pool(const ExPolygons& base_plate,
+void create_base_pool(const Polygons& base_plate,
                       TriangleMesh& output_mesh,
+                      const ExPolygons& holes,
                       const PoolConfig& = PoolConfig());
 
-/// TODO: Currently the base plate of the pool will have half the height of the
-/// whole pool. So the carved out space has also half the height. This is not
-/// a particularly elegant solution, the thickness should be exactly
-/// min_wall_thickness and it should be corrected in the future. This method
-/// will return the correct value for further processing.
+/// Returns the elevation needed for compensating the pad.
 inline double get_pad_elevation(const PoolConfig& cfg) {
     return cfg.min_wall_thickness_mm;
 }
diff --git a/src/libslic3r/SLA/SLACommon.hpp b/src/libslic3r/SLA/SLACommon.hpp
index 855802759..874388e05 100644
--- a/src/libslic3r/SLA/SLACommon.hpp
+++ b/src/libslic3r/SLA/SLACommon.hpp
@@ -43,6 +43,8 @@ struct SupportPoint {
 
     bool operator==(const SupportPoint& sp) const { return (pos==sp.pos) && head_front_radius==sp.head_front_radius && is_new_island==sp.is_new_island; }
     bool operator!=(const SupportPoint& sp) const { return !(sp == (*this)); }
+
+	template<class Archive> void serialize(Archive &ar) { ar(pos, head_front_radius, is_new_island); }
 };
 
 /// An index-triangle structure for libIGL functions. Also serves as an
@@ -60,7 +62,7 @@ class EigenMesh3D {
 
     Eigen::MatrixXd m_V;
     Eigen::MatrixXi m_F;
-    double m_ground_level = 0;
+    double m_ground_level = 0, m_gnd_offset = 0;
 
     std::unique_ptr<AABBImpl> m_aabb;
 public:
@@ -71,7 +73,9 @@ public:
 
     ~EigenMesh3D();
 
-    inline double ground_level() const { return m_ground_level; }
+    inline double ground_level() const { return m_ground_level + m_gnd_offset; }
+    inline void ground_level_offset(double o) { m_gnd_offset = o; }
+    inline double ground_level_offset() const { return m_gnd_offset; }
 
     inline const Eigen::MatrixXd& V() const { return m_V; }
     inline const Eigen::MatrixXi& F() const { return m_F; }
@@ -149,6 +153,12 @@ public:
 #endif /* SLIC3R_SLA_NEEDS_WINDTREE */
 
     double squared_distance(const Vec3d& p, int& i, Vec3d& c) const;
+    inline double squared_distance(const Vec3d &p) const
+    {
+        int   i;
+        Vec3d c;
+        return squared_distance(p, i, c);
+    }
 };
 
 
diff --git a/src/libslic3r/SLA/SLASpatIndex.hpp b/src/libslic3r/SLA/SLASpatIndex.hpp
index e5fbfa7d4..90dcdc362 100644
--- a/src/libslic3r/SLA/SLASpatIndex.hpp
+++ b/src/libslic3r/SLA/SLASpatIndex.hpp
@@ -7,13 +7,15 @@
 
 #include <Eigen/Geometry>
 
+#include <libslic3r/BoundingBox.hpp>
+
 namespace Slic3r {
 namespace sla {
 
 typedef Eigen::Matrix<double,   3, 1, Eigen::DontAlign> Vec3d;
-using SpatElement = std::pair<Vec3d, unsigned>;
+using PointIndexEl = std::pair<Vec3d, unsigned>;
 
-class SpatIndex {
+class PointIndex {
     class Impl;
 
     // We use Pimpl because it takes a long time to compile boost headers which
@@ -21,30 +23,67 @@ class SpatIndex {
     std::unique_ptr<Impl> m_impl;
 public:
 
-    SpatIndex();
-    ~SpatIndex();
+    PointIndex();
+    ~PointIndex();
 
-    SpatIndex(const SpatIndex&);
-    SpatIndex(SpatIndex&&);
-    SpatIndex& operator=(const SpatIndex&);
-    SpatIndex& operator=(SpatIndex&&);
+    PointIndex(const PointIndex&);
+    PointIndex(PointIndex&&);
+    PointIndex& operator=(const PointIndex&);
+    PointIndex& operator=(PointIndex&&);
 
-    void insert(const SpatElement&);
-    bool remove(const SpatElement&);
+    void insert(const PointIndexEl&);
+    bool remove(const PointIndexEl&);
 
     inline void insert(const Vec3d& v, unsigned idx)
     {
         insert(std::make_pair(v, unsigned(idx)));
     }
 
-    std::vector<SpatElement> query(std::function<bool(const SpatElement&)>);
-    std::vector<SpatElement> nearest(const Vec3d&, unsigned k);
+    std::vector<PointIndexEl> query(std::function<bool(const PointIndexEl&)>);
+    std::vector<PointIndexEl> nearest(const Vec3d&, unsigned k);
 
     // For testing
     size_t size() const;
     bool empty() const { return size() == 0; }
 
-    void foreach(std::function<void(const SpatElement& el)> fn);
+    void foreach(std::function<void(const PointIndexEl& el)> fn);
+};
+
+using BoxIndexEl = std::pair<Slic3r::BoundingBox, unsigned>;
+
+class BoxIndex {
+    class Impl;
+    
+    // We use Pimpl because it takes a long time to compile boost headers which
+    // is the engine of this class. We include it only in the cpp file.
+    std::unique_ptr<Impl> m_impl;
+public:
+    
+    BoxIndex();
+    ~BoxIndex();
+    
+    BoxIndex(const BoxIndex&);
+    BoxIndex(BoxIndex&&);
+    BoxIndex& operator=(const BoxIndex&);
+    BoxIndex& operator=(BoxIndex&&);
+    
+    void insert(const BoxIndexEl&);
+    inline void insert(const BoundingBox& bb, unsigned idx)
+    {
+        insert(std::make_pair(bb, unsigned(idx)));
+    }
+    
+    bool remove(const BoxIndexEl&);
+
+    enum QueryType { qtIntersects, qtWithin };
+
+    std::vector<BoxIndexEl> query(const BoundingBox&, QueryType qt);
+    
+    // For testing
+    size_t size() const;
+    bool empty() const { return size() == 0; }
+    
+    void foreach(std::function<void(const BoxIndexEl& el)> fn);
 };
 
 }
diff --git a/src/libslic3r/SLA/SLASupportTree.cpp b/src/libslic3r/SLA/SLASupportTree.cpp
index ae033c62f..4751dad6c 100644
--- a/src/libslic3r/SLA/SLASupportTree.cpp
+++ b/src/libslic3r/SLA/SLASupportTree.cpp
@@ -9,10 +9,12 @@
 #include "SLASpatIndex.hpp"
 #include "SLABasePool.hpp"
 
+#include <libslic3r/MTUtils.hpp>
 #include <libslic3r/ClipperUtils.hpp>
 #include <libslic3r/Model.hpp>
 
 #include <libnest2d/optimizers/nlopt/genetic.hpp>
+#include <libnest2d/optimizers/nlopt/subplex.hpp>
 #include <boost/log/trivial.hpp>
 #include <tbb/parallel_for.h>
 #include <libslic3r/I18N.hpp>
@@ -413,7 +415,7 @@ struct Pillar {
         assert(steps > 0);
 
         height = jp(Z) - endp(Z);
-        if(height > 0) { // Endpoint is below the starting point
+        if(height > EPSILON) { // Endpoint is below the starting point
 
             // We just create a bridge geometry with the pillar parameters and
             // move the data.
@@ -528,6 +530,7 @@ struct CompactBridge {
                   const Vec3d& ep,
                   const Vec3d& n,
                   double r,
+                  bool endball = true,
                   size_t steps = 45)
     {
         Vec3d startp = sp + r * n;
@@ -541,12 +544,14 @@ struct CompactBridge {
         double fa = 2*PI/steps;
         auto upperball = sphere(r, Portion{PI / 2 - fa, PI}, fa);
         for(auto& p : upperball.points) p += startp;
-
-        auto lowerball = sphere(r, Portion{0, PI/2 + 2*fa}, fa);
-        for(auto& p : lowerball.points) p += endp;
-
+        
+        if(endball) {
+            auto lowerball = sphere(r, Portion{0, PI/2 + 2*fa}, fa);
+            for(auto& p : lowerball.points) p += endp;
+            mesh.merge(lowerball);
+        }
+        
         mesh.merge(upperball);
-        mesh.merge(lowerball);
     }
 };
 
@@ -556,28 +561,111 @@ struct Pad {
     PoolConfig cfg;
     double zlevel = 0;
 
-    Pad() {}
+    Pad() = default;
 
-    Pad(const TriangleMesh& object_support_mesh,
-        const ExPolygons& baseplate,
+    Pad(const TriangleMesh& support_mesh,
+        const ExPolygons& modelbase,
         double ground_level,
         const PoolConfig& pcfg) :
         cfg(pcfg),
-        zlevel(ground_level +
-               (sla::get_pad_fullheight(pcfg) - sla::get_pad_elevation(pcfg)) )
+        zlevel(ground_level + 
+               sla::get_pad_fullheight(pcfg) -
+               sla::get_pad_elevation(pcfg))
     {
-        ExPolygons basep;
-        cfg.throw_on_cancel();
+        Polygons basep;
+        auto &thr = cfg.throw_on_cancel;
+        
+        thr();
+        
+        // Get a sample for the pad from the support mesh
+        {
+            ExPolygons platetmp;
 
-        // The 0.1f is the layer height with which the mesh is sampled and then
-        // the layers are unified into one vector of polygons.
-        base_plate(object_support_mesh, basep,
-                   float(cfg.min_wall_height_mm + cfg.min_wall_thickness_mm),
-                   0.1f, pcfg.throw_on_cancel);
+            float zstart = float(zlevel);
+            float zend   = zstart + float(get_pad_fullheight(pcfg) + EPSILON);
 
-        for(auto& bp : baseplate) basep.emplace_back(bp);
+            base_plate(support_mesh, platetmp, grid(zstart, zend, 0.1f), thr);
+
+            // We don't need no... holes control...
+            for (const ExPolygon &bp : platetmp)
+                basep.emplace_back(std::move(bp.contour));
+        }
+        
+        if(pcfg.embed_object) {
+            
+            // If the zero elevation mode is ON, we need to process the model
+            // base silhouette. Create the offsetted version and punch the
+            // breaksticks across its perimeter.
+            
+            ExPolygons modelbase_offs = modelbase;
+            
+            if (pcfg.embed_object.object_gap_mm > 0.0)
+                modelbase_offs
+                    = offset_ex(modelbase_offs,
+                                float(scaled(pcfg.embed_object.object_gap_mm)));
+            
+            // Create a spatial index of the support silhouette polygons.
+            // This will be used to check for intersections with the model
+            // silhouette polygons. If there is no intersection, then a certain
+            // part of the pad is redundant as it does not host any supports.
+            BoxIndex bindex;
+            {
+                unsigned idx = 0;
+                for(auto &bp : basep) {
+                    auto bb = bp.bounding_box();
+                    bb.offset(float(scaled(pcfg.min_wall_thickness_mm)));
+                    bindex.insert(bb, idx++);
+                }
+            }
+            
+            // Punching the breaksticks across the offsetted polygon perimeters
+            ExPolygons pad_stickholes; pad_stickholes.reserve(modelbase.size());
+            for(auto& poly : modelbase_offs) {
+                
+                std::vector<BoxIndexEl> qres =
+                    bindex.query(poly.contour.bounding_box(),
+                                 BoxIndex::qtIntersects);
+                    
+                if (!qres.empty()) {
+                    
+                    // The model silhouette polygon 'poly' HAS an intersection
+                    // with the support silhouettes. Include this polygon
+                    // in the pad holes with the breaksticks and merge the
+                    // original (offsetted) version with the rest of the pad
+                    // base plate.
+                    
+                    basep.emplace_back(poly.contour);
+                    
+                    // The holes of 'poly' will become positive parts of the
+                    // pad, so they has to be checked for intersections as well
+                    // and erased if there is no intersection with the supports
+                    auto it = poly.holes.begin();
+                    while(it != poly.holes.end()) {
+                        if (bindex.query(it->bounding_box(),
+                                         BoxIndex::qtIntersects).empty())
+                            it = poly.holes.erase(it);
+                        else
+                            ++it;
+                    }
+                    
+                    // Punch the breaksticks
+                    sla::breakstick_holes(
+                        poly,
+                        pcfg.embed_object.object_gap_mm,   // padding
+                        pcfg.embed_object.stick_stride_mm,
+                        pcfg.embed_object.stick_width_mm,
+                        pcfg.embed_object.stick_penetration_mm);
+                    
+                    pad_stickholes.emplace_back(poly);
+                }
+            }
+            
+            create_base_pool(basep, tmesh, pad_stickholes, cfg);
+        } else {
+            for (const ExPolygon &bp : modelbase) basep.emplace_back(bp.contour);
+            create_base_pool(basep, tmesh, {}, cfg);
+        }
 
-        create_base_pool(basep, tmesh, cfg);
         tmesh.translate(0, 0, float(zlevel));
     }
 
@@ -603,7 +691,7 @@ inline Vec2d to_vec2(const Vec3d& v3) {
     return {v3(X), v3(Y)};
 }
 
-bool operator==(const SpatElement& e1, const SpatElement& e2) {
+bool operator==(const PointIndexEl& e1, const PointIndexEl& e2) {
     return e1.second == e2.second;
 }
 
@@ -620,7 +708,7 @@ ClusteredPoints cluster(const PointSet& points,
 ClusteredPoints cluster(
         const std::vector<unsigned>& indices,
         std::function<Vec3d(unsigned)> pointfn,
-        std::function<bool(const SpatElement&, const SpatElement&)> predicate,
+        std::function<bool(const PointIndexEl&, const PointIndexEl&)> predicate,
         unsigned max_points);
 
 // This class will hold the support tree meshes with some additional bookkeeping
@@ -763,9 +851,9 @@ public:
     }
 
     const Pad& create_pad(const TriangleMesh& object_supports,
-                          const ExPolygons& baseplate,
+                          const ExPolygons& modelbase,
                           const PoolConfig& cfg) {
-        m_pad = Pad(object_supports, baseplate, ground_level, cfg);
+        m_pad = Pad(object_supports, modelbase, ground_level, cfg);
         return m_pad;
     }
 
@@ -808,7 +896,6 @@ public:
             merged.merge(bs.mesh);
         }
 
-
         if(m_ctl.stopcondition()) {
             // In case of failure we have to return an empty mesh
             meshcache = TriangleMesh();
@@ -819,7 +906,7 @@ public:
 
         // The mesh will be passed by const-pointer to TriangleMeshSlicer,
         // which will need this.
-        meshcache.require_shared_vertices();
+        if (!meshcache.empty()) meshcache.require_shared_vertices();
 
         // TODO: Is this necessary?
         //meshcache.repair();
@@ -947,7 +1034,7 @@ class SLASupportTree::Algorithm {
     ThrowOnCancel m_thr;
 
     // A spatial index to easily find strong pillars to connect to.
-    SpatIndex m_pillar_index;
+    PointIndex m_pillar_index;
 
     inline double ray_mesh_intersect(const Vec3d& s,
                                      const Vec3d& dir)
@@ -1149,7 +1236,7 @@ class SLASupportTree::Algorithm {
             auto hr = m.query_ray_hit(p + sd*dir, dir);
 
             if(ins_check && hr.is_inside()) {
-                if(hr.distance() > r + sd) hits[i] = HitResult(0.0);
+                if(hr.distance() > 2 * r + sd) hits[i] = HitResult(0.0);
                 else {
                     // re-cast the ray from the outside of the object
                     auto hr2 =
@@ -1264,9 +1351,12 @@ class SLASupportTree::Algorithm {
 
     // For connecting a head to a nearby pillar.
     bool connect_to_nearpillar(const Head& head, long nearpillar_id) {
-
-        auto nearpillar = [this, nearpillar_id]() { return m_result.pillar(nearpillar_id); };
-        if(nearpillar().bridges > m_cfg.max_bridges_on_pillar) return false;
+        
+        auto nearpillar = [this, nearpillar_id]() {
+            return m_result.pillar(nearpillar_id);
+        };
+        
+        if (nearpillar().bridges > m_cfg.max_bridges_on_pillar) return false;
 
         Vec3d headjp = head.junction_point();
         Vec3d nearjp_u = nearpillar().startpoint();
@@ -1337,7 +1427,7 @@ class SLASupportTree::Algorithm {
     }
 
     bool search_pillar_and_connect(const Head& head) {
-        SpatIndex spindex = m_pillar_index;
+        PointIndex spindex = m_pillar_index;
 
         long nearest_id = -1;
 
@@ -1369,6 +1459,120 @@ class SLASupportTree::Algorithm {
 
         return nearest_id >= 0;
     }
+    
+    // This is a proxy function for pillar creation which will mind the gap
+    // between the pad and the model bottom in zero elevation mode.
+    void create_ground_pillar(const Vec3d &jp,
+                              const Vec3d &sourcedir,
+                              double       radius,
+                              int          head_id = -1)
+    {
+        // People were killed for this number (seriously)
+        static const double SQR2 = std::sqrt(2.0);
+        static const Vec3d  DOWN = {0.0, 0.0, -1.0};
+
+        double gndlvl       = m_result.ground_level;
+        Vec3d  endp         = {jp(X), jp(Y), gndlvl};
+        double sd           = m_cfg.pillar_base_safety_distance_mm;
+        int    pillar_id    = -1;
+        double min_dist     = sd + m_cfg.base_radius_mm + EPSILON;
+        double dist         = 0;
+        bool   can_add_base = true;
+        bool   normal_mode  = true;
+
+        if (m_cfg.object_elevation_mm < EPSILON
+            && (dist = std::sqrt(m_mesh.squared_distance(endp))) < min_dist) {
+            // Get the distance from the mesh. This can be later optimized
+            // to get the distance in 2D plane because we are dealing with
+            // the ground level only.
+
+            normal_mode     = false;
+            double mv       = min_dist - dist;
+            double azimuth  = std::atan2(sourcedir(Y), sourcedir(X));
+            double sinpolar = std::sin(PI - m_cfg.bridge_slope);
+            double cospolar = std::cos(PI - m_cfg.bridge_slope);
+            double cosazm   = std::cos(azimuth);
+            double sinazm   = std::sin(azimuth);
+
+            auto dir = Vec3d(cosazm * sinpolar, sinazm * sinpolar, cospolar)
+                           .normalized();
+
+            using namespace libnest2d::opt;
+            StopCriteria scr;
+            scr.stop_score = min_dist;
+            SubplexOptimizer solver(scr);
+
+            auto result = solver.optimize_max(
+                [this, dir, jp, gndlvl](double mv) {
+                    Vec3d endp = jp + SQR2 * mv * dir;
+                    endp(Z)    = gndlvl;
+                    return std::sqrt(m_mesh.squared_distance(endp));
+                },
+                initvals(mv), bound(0.0, 2 * min_dist));
+
+            mv           = std::get<0>(result.optimum);
+            endp         = jp + SQR2 * mv * dir;
+            Vec3d pgnd   = {endp(X), endp(Y), gndlvl};
+            can_add_base = result.score > min_dist;
+            
+            double gnd_offs = m_mesh.ground_level_offset();
+            auto abort_in_shame =
+                [gnd_offs, &normal_mode, &can_add_base, &endp, jp, gndlvl]()
+            {
+                normal_mode  = true;
+                can_add_base = false;   // Nothing left to do, hope for the best
+                endp         = {jp(X), jp(Y), gndlvl - gnd_offs };
+            };
+
+            // We have to check if the bridge is feasible.
+            if (bridge_mesh_intersect(jp, dir, radius) < (endp - jp).norm())
+                abort_in_shame();
+            else {
+                // If the new endpoint is below ground, do not make a pillar
+                if (endp(Z) < gndlvl)
+                    endp = endp - SQR2 * (gndlvl - endp(Z)) * dir; // back off
+                else {
+                    
+                    auto hit = bridge_mesh_intersect(endp, DOWN, radius);
+                    if (!std::isinf(hit.distance())) abort_in_shame();
+
+                    Pillar &plr = m_result.add_pillar(endp, pgnd, radius);
+
+                    if (can_add_base)
+                        plr.add_base(m_cfg.base_height_mm,
+                                     m_cfg.base_radius_mm);
+
+                    pillar_id = plr.id;
+                }
+
+                m_result.add_bridge(jp, endp, radius);
+                m_result.add_junction(endp, radius);
+
+                // Add a degenerated pillar and the bridge.
+                // The degenerate pillar will have zero length and it will
+                // prevent from queries of head_pillar() to have non-existing
+                // pillar when the head should have one.
+                if (head_id >= 0)
+                    m_result.add_pillar(unsigned(head_id), jp, radius);
+            }
+        }
+        
+        if (normal_mode) {
+            Pillar &plr = head_id >= 0
+                              ? m_result.add_pillar(unsigned(head_id),
+                                                    endp,
+                                                    radius)
+                              : m_result.add_pillar(jp, endp, radius);
+
+            if (can_add_base)
+                plr.add_base(m_cfg.base_height_mm, m_cfg.base_radius_mm);
+
+            pillar_id = plr.id;
+        } 
+            
+        if(pillar_id >= 0) // Save the pillar endpoint in the spatial index
+            m_pillar_index.insert(endp, pillar_id);
+    }
 
 public:
 
@@ -1447,9 +1651,9 @@ public:
             // (Quaternion::FromTwoVectors) and apply the rotation to the
             // arrow head.
 
-            double z = n(2);
-            double r = 1.0;     // for normalized vector
-            double polar = std::acos(z / r);
+            double z       = n(2);
+            double r       = 1.0; // for normalized vector
+            double polar   = std::acos(z / r);
             double azimuth = std::atan2(n(1), n(0));
 
             // skip if the tilt is not sane
@@ -1473,14 +1677,14 @@ public:
                                 std::cos(polar)).normalized();
 
                 // check available distance
-                double t = pinhead_mesh_intersect(
-                                  hp, // touching point
-                                  nn, // normal
-                                  pin_r,
-                                  m_cfg.head_back_radius_mm,
-                                  w);
+                EigenMesh3D::hit_result t
+                    = pinhead_mesh_intersect(hp, // touching point
+                                             nn, // normal
+                                             pin_r,
+                                             m_cfg.head_back_radius_mm,
+                                             w);
 
-                if(t <= w) {
+                if(t.distance() <= w) {
 
                     // Let's try to optimize this angle, there might be a
                     // viable normal that doesn't collide with the model
@@ -1523,12 +1727,17 @@ public:
                 // save the verified and corrected normal
                 m_support_nmls.row(fidx) = nn;
 
-                if(t > w) {
-                    // mark the point for needing a head.
-                    m_iheads.emplace_back(fidx);
-                } else if( polar >= 3*PI/4 ) {
-                    // Headless supports do not tilt like the headed ones so
-                    // the normal should point almost to the ground.
+                if (t.distance() > w) {
+                    // Check distance from ground, we might have zero elevation.
+                    if (hp(Z) + w * nn(Z) < m_result.ground_level) {
+                        m_iheadless.emplace_back(fidx);
+                    } else {
+                        // mark the point for needing a head.
+                        m_iheads.emplace_back(fidx);
+                    }
+                } else if (polar >= 3 * PI / 4) {
+                    // Headless supports do not tilt like the headed ones
+                    // so the normal should point almost to the ground.
                     m_iheadless.emplace_back(fidx);
                 }
             }
@@ -1594,16 +1803,22 @@ public:
         // from each other in the XY plane to not cross their pillar bases
         // These clusters of support points will join in one pillar,
         // possibly in their centroid support point.
+        
         auto pointfn = [this](unsigned i) {
             return m_result.head(i).junction_point();
         };
-        auto predicate = [this](const SpatElement& e1, const SpatElement& e2) {
+
+        auto predicate = [this](const PointIndexEl &e1,
+                                const PointIndexEl &e2) {
             double d2d = distance(to_2d(e1.first), to_2d(e2.first));
             double d3d = distance(e1.first, e2.first);
-            return d2d < 2 * m_cfg.base_radius_mm &&
-                   d3d < m_cfg.max_bridge_length_mm;
+            return d2d < 2 * m_cfg.base_radius_mm
+                   && d3d < m_cfg.max_bridge_length_mm;
         };
-        m_pillar_clusters = cluster(ground_head_indices, pointfn, predicate,
+
+        m_pillar_clusters = cluster(ground_head_indices,
+                                    pointfn,
+                                    predicate,
                                     m_cfg.max_bridges_on_pillar);
     }
 
@@ -1615,7 +1830,7 @@ public:
     void routing_to_ground()
     {
         const double pradius = m_cfg.head_back_radius_mm;
-        const double gndlvl = m_result.ground_level;
+        // const double gndlvl = m_result.ground_level;
 
         ClusterEl cl_centroids;
         cl_centroids.reserve(m_pillar_clusters.size());
@@ -1648,13 +1863,8 @@ public:
 
             Head& h = m_result.head(hid);
             h.transform();
-            Vec3d p = h.junction_point(); p(Z) = gndlvl;
-            auto& plr = m_result.add_pillar(hid, p, h.r_back_mm)
-                                .add_base(m_cfg.base_height_mm,
-                                          m_cfg.base_radius_mm);
 
-            // Save the pillar endpoint and the pillar id in the spatial index
-            m_pillar_index.insert(plr.endpoint(), unsigned(plr.id));
+            create_ground_pillar(h.junction_point(), h.dir, h.r_back_mm, h.id);
         }
 
         // now we will go through the clusters ones again and connect the
@@ -1681,15 +1891,12 @@ public:
                    !search_pillar_and_connect(sidehead))
                 {
                     Vec3d pstart = sidehead.junction_point();
-                    Vec3d pend = Vec3d{pstart(X), pstart(Y), gndlvl};
+                    //Vec3d pend = Vec3d{pstart(X), pstart(Y), gndlvl};
                     // Could not find a pillar, create one
-                    auto& pillar = m_result.add_pillar(unsigned(sidehead.id),
-                                                       pend, pradius)
-                                           .add_base(m_cfg.base_height_mm,
-                                                     m_cfg.base_radius_mm);
-
-                    // connects to ground, eligible for bridging
-                    m_pillar_index.insert(pend, unsigned(pillar.id));
+                    create_ground_pillar(pstart,
+                                         sidehead.dir,
+                                         pradius,
+                                         sidehead.id);
                 }
             }
         }
@@ -1718,12 +1925,7 @@ public:
             m_result.add_bridge(hjp, endp, head.r_back_mm);
             m_result.add_junction(endp, head.r_back_mm);
 
-            auto groundp = endp;
-            groundp(Z) = m_result.ground_level;
-            auto& newpillar = m_result.add_pillar(endp, groundp, head.r_back_mm)
-                                      .add_base(m_cfg.base_height_mm,
-                                                m_cfg.base_radius_mm);
-            m_pillar_index.insert(groundp, unsigned(newpillar.id));
+            this->create_ground_pillar(endp, dir, head.r_back_mm);
         };
 
         std::vector<unsigned> modelpillars;
@@ -1883,6 +2085,28 @@ public:
             m_pillar_index.insert(pillar.endpoint(), pillid);
         }
     }
+    
+    // Helper function for interconnect_pillars where pairs of already connected
+    // pillars should be checked for not to be processed again. This can be done
+    // in O(log) or even constant time with a set or an unordered set of hash
+    // values uniquely representing a pair of integers. The order of numbers
+    // within the pair should not matter, it has the same unique hash.
+    template<class I> static I pairhash(I a, I b)
+    {
+        using std::ceil; using std::log2; using std::max; using std::min;
+        
+        static_assert(std::is_integral<I>::value,
+                      "This function works only for integral types.");
+
+        I g = min(a, b), l = max(a, b);
+        
+        auto bits_g = g ? int(ceil(log2(g))) : 0;
+
+        // Assume the hash will fit into the output variable
+        assert((l ? (ceil(log2(l))) : 0) + bits_g < int(sizeof(I) * CHAR_BIT));
+        
+        return (l << bits_g) + g;
+    }
 
     void interconnect_pillars() {
         // Now comes the algorithm that connects pillars with each other.
@@ -1900,45 +2124,51 @@ public:
         double min_height_ratio = 0.5;
 
         std::set<unsigned long> pairs;
-
+        
+        // A function to connect one pillar with its neighbors. THe number of
+        // neighbors is given in the configuration. This function if called
+        // for every pillar in the pillar index. A pair of pillar will not
+        // be connected multiple times this is ensured by the 'pairs' set which
+        // remembers the processed pillar pairs
         auto cascadefn =
-                [this, d, &pairs, min_height_ratio, H1] (const SpatElement& el)
+                [this, d, &pairs, min_height_ratio, H1] (const PointIndexEl& el)
         {
-            Vec3d qp = el.first;
-
-            const Pillar& pillar = m_result.pillar(el.second);
+            Vec3d qp = el.first;    // endpoint of the pillar
 
+            const Pillar& pillar = m_result.pillar(el.second); // actual pillar
+            
+            // Get the max number of neighbors a pillar should connect to
             unsigned neighbors = m_cfg.pillar_cascade_neighbors;
 
-            // connections are enough for one pillar
+            // connections are already enough for the pillar
             if(pillar.links >= neighbors) return;
 
             // Query all remaining points within reach
-            auto qres = m_pillar_index.query([qp, d](const SpatElement& e){
+            auto qres = m_pillar_index.query([qp, d](const PointIndexEl& e){
                 return distance(e.first, qp) < d;
             });
 
             // sort the result by distance (have to check if this is needed)
             std::sort(qres.begin(), qres.end(),
-                      [qp](const SpatElement& e1, const SpatElement& e2){
+                      [qp](const PointIndexEl& e1, const PointIndexEl& e2){
                 return distance(e1.first, qp) < distance(e2.first, qp);
             });
 
-            for(auto& re : qres) {
+            for(auto& re : qres) { // process the queried neighbors
 
-                if(re.second == el.second) continue;
+                if(re.second == el.second) continue; // Skip self
 
                 auto a = el.second, b = re.second;
 
-                // I hope that the area of a square is never equal to its
-                // circumference
-                auto hashval = 2 * (a + b) + a * b;
-
+                // Get unique hash for the given pair (order doesn't matter)
+                auto hashval = pairhash(a, b);
+                
+                // Search for the pair amongst the remembered pairs
                 if(pairs.find(hashval) != pairs.end()) continue;
 
                 const Pillar& neighborpillar = m_result.pillars()[re.second];
 
-                // this neighbor is occupied
+                // this neighbor is occupied, skip
                 if(neighborpillar.links >= neighbors) continue;
 
                 if(interconnect(pillar, neighborpillar)) {
@@ -1960,47 +2190,79 @@ public:
                 if(pillar.links >= neighbors) break;
             }
         };
-
+        
+        // Run the cascade for the pillars in the index
         m_pillar_index.foreach(cascadefn);
-
+       
+        // We would be done here if we could allow some pillars to not be
+        // connected with any neighbors. But this might leave the support tree
+        // unprintable.
+        //
+        // The current solution is to insert additional pillars next to these
+        // lonely pillars. One or even two additional pillar might get inserted
+        // depending on the length of the lonely pillar.
+        
         size_t pillarcount = m_result.pillars().size();
-
+        
+        // Again, go through all pillars, this time in the whole support tree
+        // not just the index.
         for(size_t pid = 0; pid < pillarcount; pid++) {
             auto pillar = [this, pid]() { return m_result.pillar(pid); };
-
+           
+            // Decide how many additional pillars will be needed:
+            
             unsigned needpillars = 0;
-            if(pillar().bridges > m_cfg.max_bridges_on_pillar) needpillars = 3;
-            else if(pillar().links < 2 && pillar().height > H2) {
+            if (pillar().bridges > m_cfg.max_bridges_on_pillar)
+                needpillars = 3;
+            else if (pillar().links < 2 && pillar().height > H2) {
                 // Not enough neighbors to support this pillar
                 needpillars = 2 - pillar().links;
-            }
-            else if(pillar().links < 1 && pillar().height > H1) {
+            } else if (pillar().links < 1 && pillar().height > H1) {
                 // No neighbors could be found and the pillar is too long.
                 needpillars = 1;
             }
 
-            // Search for new pillar locations
-            bool found = false;
-            double alpha = 0; // goes to 2Pi
-            double r = 2 * m_cfg.base_radius_mm;
-            Vec3d pillarsp = pillar().startpoint();
+            // Search for new pillar locations:
+
+            bool   found    = false;
+            double alpha    = 0; // goes to 2Pi
+            double r        = 2 * m_cfg.base_radius_mm;
+            Vec3d  pillarsp = pillar().startpoint();
+
+            // temp value for starting point detection
             Vec3d sp(pillarsp(X), pillarsp(Y), pillarsp(Z) - r);
-            std::vector<bool> tv(needpillars, false);
-            std::vector<Vec3d> spts(needpillars);
 
-            while(!found && alpha < 2*PI) {
+            // A vector of bool for placement feasbility
+            std::vector<bool>  canplace(needpillars, false);
+            std::vector<Vec3d> spts(needpillars); // vector of starting points
 
-                for(unsigned n = 0; n < needpillars; n++) {
-                    double a = alpha + n * PI/3;
-                    Vec3d s = sp;
+            double gnd      = m_result.ground_level;
+            double min_dist = m_cfg.pillar_base_safety_distance_mm +
+                              m_cfg.base_radius_mm + EPSILON;
+            
+            while(!found && alpha < 2*PI) {
+                for (unsigned n = 0;
+                     n < needpillars && (!n || canplace[n - 1]);
+                     n++)
+                {
+                    double a = alpha + n * PI / 3;
+                    Vec3d  s = sp;
                     s(X) += std::cos(a) * r;
                     s(Y) += std::sin(a) * r;
                     spts[n] = s;
+                    
+                    // Check the path vertically down                    
                     auto hr = bridge_mesh_intersect(s, {0, 0, -1}, pillar().r);
-                    tv[n] = std::isinf(hr.distance());
+                    Vec3d gndsp{s(X), s(Y), gnd};
+                    
+                    // If the path is clear, check for pillar base collisions
+                    canplace[n] = std::isinf(hr.distance()) &&
+                                  std::sqrt(m_mesh.squared_distance(gndsp)) >
+                                      min_dist;
                 }
 
-                found = std::all_of(tv.begin(), tv.end(), [](bool v){return v;});
+                found = std::all_of(canplace.begin(), canplace.end(),
+                                    [](bool v) { return v; });
 
                 // 20 angles will be tried...
                 alpha += 0.1 * PI;
@@ -2010,7 +2272,7 @@ public:
             newpills.reserve(needpillars);
 
             if(found) for(unsigned n = 0; n < needpillars; n++) {
-                Vec3d s = spts[n]; double gnd = m_result.ground_level;
+                Vec3d s = spts[n]; 
                 Pillar p(s, Vec3d(s(X), s(Y), gnd), pillar().r);
                 p.add_base(m_cfg.base_height_mm, m_cfg.base_radius_mm);
 
@@ -2075,9 +2337,13 @@ public:
             // This is only for checking
             double idist = bridge_mesh_intersect(sph, dir, R, true);
             double dist = ray_mesh_intersect(sj, dir);
+            if (std::isinf(dist))
+                dist = sph(Z) - m_mesh.ground_level()
+                       + m_mesh.ground_level_offset();
 
-            if(std::isinf(idist) || std::isnan(idist) || idist < 2*R ||
-               std::isinf(dist)  || std::isnan(dist)   || dist < 2*R) {
+            if(std::isnan(idist) || idist < 2*R ||
+               std::isnan(dist)  || dist  < 2*R)
+            {
                 BOOST_LOG_TRIVIAL(warning) << "Can not find route for headless"
                                            << " support stick at: "
                                            << sj.transpose();
@@ -2085,7 +2351,7 @@ public:
             }
 
             Vec3d ej = sj + (dist + HWIDTH_MM)* dir;
-            m_result.add_compact_bridge(sp, ej, n, R);
+            m_result.add_compact_bridge(sp, ej, n, R, !std::isinf(dist));
         }
     }
 };
@@ -2214,7 +2480,9 @@ bool SLASupportTree::generate(const std::vector<SupportPoint> &support_points,
     return pc == ABORT;
 }
 
-SLASupportTree::SLASupportTree(): m_impl(new Impl()) {}
+SLASupportTree::SLASupportTree(double gnd_lvl): m_impl(new Impl()) {
+    m_impl->ground_level = gnd_lvl;
+}
 
 const TriangleMesh &SLASupportTree::merged_mesh() const
 {
@@ -2226,7 +2494,7 @@ void SLASupportTree::merged_mesh_with_pad(TriangleMesh &outmesh) const {
     outmesh.merge(get_pad());
 }
 
-SlicedSupports SLASupportTree::slice(float layerh, float init_layerh) const
+std::vector<ExPolygons> SLASupportTree::slice(float layerh, float init_layerh) const
 {
     if(init_layerh < 0) init_layerh = layerh;
     auto& stree = get();
@@ -2245,36 +2513,31 @@ SlicedSupports SLASupportTree::slice(float layerh, float init_layerh) const
 
     TriangleMesh fullmesh = m_impl->merged_mesh();
     fullmesh.merge(get_pad());
-    fullmesh.require_shared_vertices(); // TriangleMeshSlicer needs this
+    if (!fullmesh.empty()) fullmesh.require_shared_vertices();
     TriangleMeshSlicer slicer(&fullmesh);
-    SlicedSupports ret;
+    std::vector<ExPolygons> ret;
     slicer.slice(heights, 0.f, &ret, get().ctl().cancelfn);
 
     return ret;
 }
 
-SlicedSupports SLASupportTree::slice(const std::vector<float> &heights,
+std::vector<ExPolygons> SLASupportTree::slice(const std::vector<float> &heights,
                                      float cr) const
 {
     TriangleMesh fullmesh = m_impl->merged_mesh();
     fullmesh.merge(get_pad());
-    fullmesh.require_shared_vertices(); // TriangleMeshSlicer needs this
+    if (!fullmesh.empty()) fullmesh.require_shared_vertices();
     TriangleMeshSlicer slicer(&fullmesh);
-    SlicedSupports ret;
+    std::vector<ExPolygons> ret;
     slicer.slice(heights, cr, &ret, get().ctl().cancelfn);
 
     return ret;
 }
 
-const TriangleMesh &SLASupportTree::add_pad(const SliceLayer& baseplate,
+const TriangleMesh &SLASupportTree::add_pad(const ExPolygons& modelbase,
                                             const PoolConfig& pcfg) const
 {
-//    PoolConfig pcfg;
-//    pcfg.min_wall_thickness_mm = min_wall_thickness_mm;
-//    pcfg.min_wall_height_mm    = min_wall_height_mm;
-//    pcfg.max_merge_distance_mm = max_merge_distance_mm;
-//    pcfg.edge_radius_mm        = edge_radius_mm;
-    return m_impl->create_pad(merged_mesh(), baseplate, pcfg).tmesh;
+    return m_impl->create_pad(merged_mesh(), modelbase, pcfg).tmesh;
 }
 
 const TriangleMesh &SLASupportTree::get_pad() const
diff --git a/src/libslic3r/SLA/SLASupportTree.hpp b/src/libslic3r/SLA/SLASupportTree.hpp
index 66677e4d7..8602d8a46 100644
--- a/src/libslic3r/SLA/SLASupportTree.hpp
+++ b/src/libslic3r/SLA/SLASupportTree.hpp
@@ -24,10 +24,11 @@ class TriangleMesh;
 class Model;
 class ModelInstance;
 class ModelObject;
+class Polygon;
 class ExPolygon;
 
-using SliceLayer = std::vector<ExPolygon>;
-using SlicedSupports = std::vector<SliceLayer>;
+using Polygons = std::vector<Polygon>;
+using ExPolygons = std::vector<ExPolygon>;
 
 namespace sla {
 
@@ -80,6 +81,10 @@ struct SupportConfig {
     // The elevation in Z direction upwards. This is the space between the pad
     // and the model object's bounding box bottom.
     double object_elevation_mm = 10;
+    
+    // The shortest distance between a pillar base perimeter from the model
+    // body. This is only useful when elevation is set to zero.
+    double pillar_base_safety_distance_mm = 0.5;
 
     // /////////////////////////////////////////////////////////////////////////
     // Compile time configuration values (candidates for runtime)
@@ -160,7 +165,7 @@ class SLASupportTree {
 
 public:
 
-    SLASupportTree();
+    SLASupportTree(double ground_level = 0.0);
 
     SLASupportTree(const std::vector<SupportPoint>& pts,
                    const EigenMesh3D& em,
@@ -179,12 +184,17 @@ public:
     void merged_mesh_with_pad(TriangleMesh&) const;
 
     /// Get the sliced 2d layers of the support geometry.
-    SlicedSupports slice(float layerh, float init_layerh = -1.0) const;
+    std::vector<ExPolygons> slice(float layerh, float init_layerh = -1.0) const;
 
-    SlicedSupports slice(const std::vector<float>&, float closing_radius) const;
+    std::vector<ExPolygons> slice(const std::vector<float> &,
+                                  float closing_radius) const;
 
     /// Adding the "pad" (base pool) under the supports
-    const TriangleMesh& add_pad(const SliceLayer& baseplate,
+    /// modelbase will be used according to the embed_object flag in PoolConfig.
+    /// If set, the plate will interpreted as the model's intrinsic pad. 
+    /// Otherwise, the modelbase will be unified with the base plate calculated
+    /// from the supports.
+    const TriangleMesh& add_pad(const ExPolygons& modelbase,
                                 const PoolConfig& pcfg) const;
 
     /// Get the pad geometry
diff --git a/src/libslic3r/SLA/SLASupportTreeIGL.cpp b/src/libslic3r/SLA/SLASupportTreeIGL.cpp
index 1609b9ac4..4b6498a20 100644
--- a/src/libslic3r/SLA/SLASupportTreeIGL.cpp
+++ b/src/libslic3r/SLA/SLASupportTreeIGL.cpp
@@ -29,69 +29,137 @@ namespace sla {
 using igl::PI;
 
 /* **************************************************************************
- * SpatIndex implementation
+ * PointIndex implementation
  * ************************************************************************** */
 
-class SpatIndex::Impl {
+class PointIndex::Impl {
 public:
-    using BoostIndex = boost::geometry::index::rtree< SpatElement,
+    using BoostIndex = boost::geometry::index::rtree< PointIndexEl,
                        boost::geometry::index::rstar<16, 4> /* ? */ >;
 
     BoostIndex m_store;
 };
 
-SpatIndex::SpatIndex(): m_impl(new Impl()) {}
-SpatIndex::~SpatIndex() {}
+PointIndex::PointIndex(): m_impl(new Impl()) {}
+PointIndex::~PointIndex() {}
 
-SpatIndex::SpatIndex(const SpatIndex &cpy): m_impl(new Impl(*cpy.m_impl)) {}
-SpatIndex::SpatIndex(SpatIndex&& cpy): m_impl(std::move(cpy.m_impl)) {}
+PointIndex::PointIndex(const PointIndex &cpy): m_impl(new Impl(*cpy.m_impl)) {}
+PointIndex::PointIndex(PointIndex&& cpy): m_impl(std::move(cpy.m_impl)) {}
 
-SpatIndex& SpatIndex::operator=(const SpatIndex &cpy)
+PointIndex& PointIndex::operator=(const PointIndex &cpy)
 {
     m_impl.reset(new Impl(*cpy.m_impl));
     return *this;
 }
 
-SpatIndex& SpatIndex::operator=(SpatIndex &&cpy)
+PointIndex& PointIndex::operator=(PointIndex &&cpy)
 {
     m_impl.swap(cpy.m_impl);
     return *this;
 }
 
-void SpatIndex::insert(const SpatElement &el)
+void PointIndex::insert(const PointIndexEl &el)
 {
     m_impl->m_store.insert(el);
 }
 
-bool SpatIndex::remove(const SpatElement& el)
+bool PointIndex::remove(const PointIndexEl& el)
 {
     return m_impl->m_store.remove(el) == 1;
 }
 
-std::vector<SpatElement>
-SpatIndex::query(std::function<bool(const SpatElement &)> fn)
+std::vector<PointIndexEl>
+PointIndex::query(std::function<bool(const PointIndexEl &)> fn)
 {
     namespace bgi = boost::geometry::index;
 
-    std::vector<SpatElement> ret;
+    std::vector<PointIndexEl> ret;
     m_impl->m_store.query(bgi::satisfies(fn), std::back_inserter(ret));
     return ret;
 }
 
-std::vector<SpatElement> SpatIndex::nearest(const Vec3d &el, unsigned k = 1)
+std::vector<PointIndexEl> PointIndex::nearest(const Vec3d &el, unsigned k = 1)
 {
     namespace bgi = boost::geometry::index;
-    std::vector<SpatElement> ret; ret.reserve(k);
+    std::vector<PointIndexEl> ret; ret.reserve(k);
     m_impl->m_store.query(bgi::nearest(el, k), std::back_inserter(ret));
     return ret;
 }
 
-size_t SpatIndex::size() const
+size_t PointIndex::size() const
 {
     return m_impl->m_store.size();
 }
 
-void SpatIndex::foreach(std::function<void (const SpatElement &)> fn)
+void PointIndex::foreach(std::function<void (const PointIndexEl &)> fn)
+{
+    for(auto& el : m_impl->m_store) fn(el);
+}
+
+/* **************************************************************************
+ * BoxIndex implementation
+ * ************************************************************************** */
+
+class BoxIndex::Impl {
+public:
+    using BoostIndex = boost::geometry::index::
+        rtree<BoxIndexEl, boost::geometry::index::rstar<16, 4> /* ? */>;
+
+    BoostIndex m_store;
+};
+
+BoxIndex::BoxIndex(): m_impl(new Impl()) {}
+BoxIndex::~BoxIndex() {}
+
+BoxIndex::BoxIndex(const BoxIndex &cpy): m_impl(new Impl(*cpy.m_impl)) {}
+BoxIndex::BoxIndex(BoxIndex&& cpy): m_impl(std::move(cpy.m_impl)) {}
+
+BoxIndex& BoxIndex::operator=(const BoxIndex &cpy)
+{
+    m_impl.reset(new Impl(*cpy.m_impl));
+    return *this;
+}
+
+BoxIndex& BoxIndex::operator=(BoxIndex &&cpy)
+{
+    m_impl.swap(cpy.m_impl);
+    return *this;
+}
+
+void BoxIndex::insert(const BoxIndexEl &el)
+{
+    m_impl->m_store.insert(el);
+}
+
+bool BoxIndex::remove(const BoxIndexEl& el)
+{
+    return m_impl->m_store.remove(el) == 1;
+}
+
+std::vector<BoxIndexEl> BoxIndex::query(const BoundingBox &qrbb,
+                                        BoxIndex::QueryType qt)
+{
+    namespace bgi = boost::geometry::index;
+    
+    std::vector<BoxIndexEl> ret; ret.reserve(m_impl->m_store.size());
+    
+    switch (qt) {
+    case qtIntersects:
+        m_impl->m_store.query(bgi::intersects(qrbb), std::back_inserter(ret));
+        break;
+    case qtWithin:
+        m_impl->m_store.query(bgi::within(qrbb), std::back_inserter(ret));
+    }
+    
+    return ret;
+}
+
+size_t BoxIndex::size() const
+{
+    return m_impl->m_store.size();
+}
+
+void BoxIndex::foreach(std::function<void (const BoxIndexEl &)> fn)
 {
     for(auto& el : m_impl->m_store) fn(el);
 }
@@ -343,12 +411,14 @@ PointSet normals(const PointSet& points,
     return ret;
 }
 namespace bgi = boost::geometry::index;
-using Index3D = bgi::rtree< SpatElement, bgi::rstar<16, 4> /* ? */ >;
+using Index3D = bgi::rtree< PointIndexEl, bgi::rstar<16, 4> /* ? */ >;
 
-ClusteredPoints cluster(Index3D& sindex, unsigned max_points,
-                        std::function<std::vector<SpatElement>(const Index3D&, const SpatElement&)> qfn)
+ClusteredPoints cluster(Index3D &sindex,
+                        unsigned max_points,
+                        std::function<std::vector<PointIndexEl>(
+                            const Index3D &, const PointIndexEl &)> qfn)
 {
-    using Elems = std::vector<SpatElement>;
+    using Elems = std::vector<PointIndexEl>;
 
     // Recursive function for visiting all the points in a given distance to
     // each other
@@ -356,8 +426,8 @@ ClusteredPoints cluster(Index3D& sindex, unsigned max_points,
     [&sindex, &group, max_points, qfn](Elems& pts, Elems& cluster)
     {
         for(auto& p : pts) {
-            std::vector<SpatElement> tmp = qfn(sindex, p);
-            auto cmp = [](const SpatElement& e1, const SpatElement& e2){
+            std::vector<PointIndexEl> tmp = qfn(sindex, p);
+            auto cmp = [](const PointIndexEl& e1, const PointIndexEl& e2){
                 return e1.second < e2.second;
             };
 
@@ -401,12 +471,12 @@ ClusteredPoints cluster(Index3D& sindex, unsigned max_points,
 }
 
 namespace {
-std::vector<SpatElement> distance_queryfn(const Index3D& sindex,
-                                          const SpatElement& p,
+std::vector<PointIndexEl> distance_queryfn(const Index3D& sindex,
+                                          const PointIndexEl& p,
                                           double dist,
                                           unsigned max_points)
 {
-    std::vector<SpatElement> tmp; tmp.reserve(max_points);
+    std::vector<PointIndexEl> tmp; tmp.reserve(max_points);
     sindex.query(
         bgi::nearest(p.first, max_points),
         std::back_inserter(tmp)
@@ -433,7 +503,7 @@ ClusteredPoints cluster(
     for(auto idx : indices) sindex.insert( std::make_pair(pointfn(idx), idx));
 
     return cluster(sindex, max_points,
-                   [dist, max_points](const Index3D& sidx, const SpatElement& p)
+                   [dist, max_points](const Index3D& sidx, const PointIndexEl& p)
     {
         return distance_queryfn(sidx, p, dist, max_points);
     });
@@ -443,7 +513,7 @@ ClusteredPoints cluster(
 ClusteredPoints cluster(
         const std::vector<unsigned>& indices,
         std::function<Vec3d(unsigned)> pointfn,
-        std::function<bool(const SpatElement&, const SpatElement&)> predicate,
+        std::function<bool(const PointIndexEl&, const PointIndexEl&)> predicate,
         unsigned max_points)
 {
     // A spatial index for querying the nearest points
@@ -453,10 +523,10 @@ ClusteredPoints cluster(
     for(auto idx : indices) sindex.insert( std::make_pair(pointfn(idx), idx));
 
     return cluster(sindex, max_points,
-        [max_points, predicate](const Index3D& sidx, const SpatElement& p)
+        [max_points, predicate](const Index3D& sidx, const PointIndexEl& p)
     {
-        std::vector<SpatElement> tmp; tmp.reserve(max_points);
-        sidx.query(bgi::satisfies([p, predicate](const SpatElement& e){
+        std::vector<PointIndexEl> tmp; tmp.reserve(max_points);
+        sidx.query(bgi::satisfies([p, predicate](const PointIndexEl& e){
             return predicate(p, e);
         }), std::back_inserter(tmp));
         return tmp;
@@ -473,7 +543,7 @@ ClusteredPoints cluster(const PointSet& pts, double dist, unsigned max_points)
         sindex.insert(std::make_pair(Vec3d(pts.row(i)), unsigned(i)));
 
     return cluster(sindex, max_points,
-                   [dist, max_points](const Index3D& sidx, const SpatElement& p)
+                   [dist, max_points](const Index3D& sidx, const PointIndexEl& p)
     {
         return distance_queryfn(sidx, p, dist, max_points);
     });