Detect too-small planar tracking patches.

The planar tracker did not detect very skinny patches which have
effectively zero area and are untrackable. This adds detection and
rejection of patterns with zero area. This fixes a crash found by
during Mango production.

2 files changed, 26 insertions, 9 deletions

diff --git a/extern/libmv/libmv/tracking/track_region.cc b/extern/libmv/libmv/tracking/track_region.cc
index 89f18afd556..41911552f6c 100644
--- a/extern/libmv/libmv/tracking/track_region.cc
+++ b/extern/libmv/libmv/tracking/track_region.cc
@@ -1123,6 +1123,9 @@ void CreateBrutePattern(const double *x1, const double *y1,
 // correlation. Instead, this is a dumb implementation. Surprisingly, it is
 // fast enough in practice.
 //
+// Returns true if any alignment was found, and false if the projected pattern
+// is zero sized.
+//
 // TODO(keir): The normalization is less effective for the brute force search
 // than it is with the Ceres solver. It's unclear if this is a bug or due to
 // the original frame being too different from the reprojected reference in the
@@ -1133,7 +1136,7 @@ void CreateBrutePattern(const double *x1, const double *y1,
 // totally different warping interface, since access to more than a the source
 // and current destination frame is necessary.
 template<typename Warp>
-void BruteTranslationOnlyInitialize(const FloatImage &image1,
+bool BruteTranslationOnlyInitialize(const FloatImage &image1,
                                     const FloatImage *image1_mask,
                                     const FloatImage &image2,
                                     const int num_extra_points,
@@ -1179,6 +1182,7 @@ void BruteTranslationOnlyInitialize(const FloatImage &image1,
   int best_c = -1;
   int w = pattern.cols();
   int h = pattern.rows();
+
   for (int r = 0; r < (image2.Height() - h); ++r) {
     for (int c = 0; c < (image2.Width() - w); ++c) {
       // Compute the weighted sum of absolute differences, Eigen style. Note
@@ -1203,8 +1207,12 @@ void BruteTranslationOnlyInitialize(const FloatImage &image1,
       }
     }
   }
-  CHECK_NE(best_r, -1);
-  CHECK_NE(best_c, -1);
+
+  // This mean the effective pattern area is zero. This check could go earlier,
+  // but this is less code.
+  if (best_r == -1 || best_c == -1) {
+    return false;
+  }
 
   LG << "Brute force translation found a shift. "
      << "best_c: " << best_c << ", best_r: " << best_r << ", "
@@ -1219,6 +1227,7 @@ void BruteTranslationOnlyInitialize(const FloatImage &image1,
     x2[i] += best_c - origin_x;
     y2[i] += best_r - origin_y;
   }
+  return true;
 }
 
 }  // namespace
@@ -1270,12 +1279,19 @@ void TemplatedTrackRegion(const FloatImage &image1,
   if (SearchAreaTooBigForDescent(image2, x2, y2) &&
       options.use_brute_initialization) {
     LG << "Running brute initialization...";
-    BruteTranslationOnlyInitialize<Warp>(image_and_gradient1,
-                                         options.image1_mask,
-                                         image2,
-                                         options.num_extra_points,
-                                         options.use_normalized_intensities,
-                                         x1, y1, x2, y2);
+    bool found_any_alignment = BruteTranslationOnlyInitialize<Warp>(
+        image_and_gradient1,
+        options.image1_mask,
+        image2,
+        options.num_extra_points,
+        options.use_normalized_intensities,
+        x1, y1, x2, y2);
+    if (!found_any_alignment) {
+      LG << "Brute failed to find an alignment; pattern too small. "
+         << "Failing entire track operation.";
+      result->termination = TrackRegionResult::INSUFFICIENT_PATTERN_AREA;
+      return;
+    }
     for (int i = 0; i < 4; ++i) {
       LG << "P" << i << ": (" << x1[i] << ", " << y1[i] << "); brute ("
          << x2[i] << ", " << y2[i] << "); (dx, dy): (" << (x2[i] - x1[i])
diff --git a/extern/libmv/libmv/tracking/track_region.h b/extern/libmv/libmv/tracking/track_region.h
index 22ecfc54a15..7cfcae6852f 100644
--- a/extern/libmv/libmv/tracking/track_region.h
+++ b/extern/libmv/libmv/tracking/track_region.h
@@ -111,6 +111,7 @@ struct TrackRegionResult {
     DESTINATION_OUT_OF_BOUNDS,
     FELL_OUT_OF_BOUNDS,
     INSUFFICIENT_CORRELATION,
+    INSUFFICIENT_PATTERN_AREA,
     CONFIGURATION_ERROR,
   };
   Termination termination;