FIX: numerical instability in KLT response

MRPT · Aug 31, 2024 · 705026c · 705026c
1 parent 301d301
commit 705026c
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diff --git a/doc/source/doxygen-docs/changelog.md b/doc/source/doxygen-docs/changelog.md
@@ -7,7 +7,7 @@
   - pymrpt:
     - Fix all C++ build warnings in pymrpt.
 - BUG FIXES:
-  - Avoid failing KLT unit tests in the loong64 architecture.
+  - Fix unstable keypoint KLT response values leading to NaN in some architectures.
   - Fix tons of typos and Debian-specific spare install files (lintian --pedantic).
   - Fix segfault in arm64 EKF unit tests.
 

diff --git a/libs/img/src/CImage.cpp b/libs/img/src/CImage.cpp
@@ -2076,8 +2076,9 @@ float CImage::KLT_response(
   // mrpt::math::detail::eigenVectorsMatrix_special_2x2():
   const float t = Gxx + Gyy;               // Trace
   const float de = Gxx * Gyy - Gxy * Gxy;  // Det
+  const float discr = std::max<float>(.0f, t * t - 4.0f * de);
   // The smallest eigenvalue is:
-  return 0.5f * (t - std::sqrt(t * t - 4.0f * de));
+  return 0.5f * (t - std::sqrt(discr));
 #else
   return 0;
 #endif