# ransacReprojThreshold?

Hello guys,

I am investigating further into RANSAC with Homography.

One thing i don't fully understand is this formula:

What **HsrcPointsi** rapresents here?

ransacReprojThreshold?

Hello guys,

I am investigating further into RANSAC with Homography.

One thing i don't fully understand is this formula:

What **HsrcPointsi** rapresents here?

add a comment

2

RANSAC gets as input a set of matches and randomly selects some of them to compute a homography H. It then tests, how many matches 'fit' to this homography. If a match is good enough, it counts as an inlier. This is repeated many times and hopefully, RANSAC will find a homography that has many inliers and thus a good score.

The above formula is the test that defines, whether a match is an inlier or not.
Given a match `m(srcPoint, dstPoint)`

and a homography `H`

, m is an outlier, if the distance between `dstPoint`

and `H*srcPoint`

(homography applied to `srcPoint`

) is greater than `ransacReprojThreshold`

.

initally i wasn't understanding it correctly because on willowgarage the documentation http://opencv.willowgarage.com/documentation/python/camera_calibration_and_3d_reconstruction.html#findhomography reports HsrcPoints (that has no mean) while on opencv.org H * srcPoints that is the correct documentation

Asked: **
2012-10-01 06:58:15 -0500
**

Seen: **2,099 times**

Last updated: **Oct 02 '12**

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