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2012-11-03 18:34:23 -0500 answered a question Are SURF feature descriptors computed differently in 2.3.1 and 2.4.2? (bug or feature ???)

I found that the SURF feature implemented in 2.4.2 is no rotation invariant. The code "descriptor_dir = fastAtan2( -besty, bestx );" in "nonfree\src\surf.cpp" line 817, which computes the feature orientation, is not correc. You can modify it to "descriptor_dir = fastAtan2( besty, bestx );" ,and rebuild the nonfree module to get the right SURF.