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Improve perfomance of median calculation in LMedS algorithm

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* Use `nth_element()` to find the median instead of `sort()` in `LMeDSPointSetRegistrator::run()`

* Improves performance of this part of LMedS from `n log(n)` to `n` by avoiding doing a full sort.

* Makes LMedS 2x faster for 100 points, 4x faster for 5,000 points in `EstimateAffine2D()`.

* LMedS is now never more than 2x slower than RANSAC and is faster in some cases.
This commit is contained in:
Matthew Self
2016-08-26 20:39:38 -07:00
parent 40b870704e
commit 7de2e1e795
1 changed files with 2 additions and 4 deletions
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modules/calib3d/src/ptsetreg.cpp
+2 -4
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@@ -344,10 +344,8 @@ public:
else
errf = err;
CV_Assert( errf.isContinuous() && errf.type() == CV_32F && (int)errf.total() == count );
std::sort(errf.ptr<int>(), errf.ptr<int>() + count);
double median = count % 2 != 0 ?
errf.at<float>(count/2) : (errf.at<float>(count/2-1) + errf.at<float>(count/2))*0.5;
std::nth_element(errf.ptr<int>(), errf.ptr<int>() + count/2, errf.ptr<int>() + count);
double median = errf.at<float>(count/2);
if( median < minMedian )
{