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Fix non-deterministic behavior in legacy findFundamentalMat with USAC methods#28199
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asmorkalov commentedDec 16, 2025
@Jatin-Y07 Thanks a lot for the bug fix. Could you add simple test that highlights the issue? |
Author
Jatin-Y07 commentedDec 16, 2025
@asmorkalov Sure, I will add the test. |
This PR have the fix of issueopencv#27388 and a simple test in test_fundam.cpp that highlights the issue.Thanks
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Summary
This PR fixes a regression reported in Issue#27388 where
findFundamentalMatproduces non-deterministic results when usingUSACmethods (e.g.,USAC_MAGSAC) in recent OpenCV versions.The Problem
In OpenCV 4.11+, the default
UsacParamsenable parallel execution (isParallel = true) and use a random seed. The legacy overload offindFundamentalMat(which takesint method) delegates to these defaults, causing the output to vary between runs even with identical inputs. This breaks behavior compatibility with older versions (e.g., 4.6.0) where results were deterministic.The Fix
This patch modifies the legacy wrapper in
modules/calib3d/src/fundam.cpp. When aUSACmethod is selected via the legacy API, we now explicitly enforce:randomGeneratorState = 0: Ensures a fixed seed is used.isParallel = false: Disables race conditions from parallel RANSAC to guarantee bit-exact reproducibility.