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pose estimation using RANSAC

asked Sep 20 '12

Nabeel gravatar image

updated Sep 20 '12

jav_rock gravatar image

Hi Hi Everyone,

As I posted before i had a problem with solvePnPRansac pose estimation. I solved that issues as I was doing something in mapping of my data.

I generate vectors of 2D points and corresponding 3D points (Top 20 matches). Then I generate a Camera Matrix =[fx 1 cx; 1 fy cy;0 0 1] and I assume distortion coefficients are zero. Then I apply solvePnPRANSAC to estimate the pose. I get inliers. I am using 10 Error Threshold in RANSAC function and run it for 200 iterations.

From pose, I reproject my points back. Some reprojected points are coming very far from actual image points. Please see the attached figure.

So I am wondering if there is any step needed before calling RANSAC to ensure good results. !

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answered Sep 20 '12

Jacek gravatar image

updated Sep 20 '12

Camera matrix = [fx 1 cx; 1 fy cy;0 0 1] is wrong it should be [fx 0 cx; 0 fy cy;0 0 1] (or [fx s cx; 0 fy cy;0 0 1] if you have a camera with non-zero skew s but this is seldom the case).

Besides the procedure you described looks OK. Only reprojection error = 10 is huge, I'm not sure if this is for purpose but you usually should use reprojection error like 1 or 2 pixels.

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hi one thing i am wondering . . can i use 0 for both cx and cy ? or should it be the centre of the image?

Nabeel gravatar imageNabeel (Oct 1 '12)edit

Hi. Just wondering if this method can lead to very accurate pose (position and orientation) estimation, Im looking for accuracy of plus-minus 1-2cm by 1m distance. Would be that possible?

astronaut gravatar imageastronaut (Jun 19 '0)edit

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Asked: Sep 20 '12

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Last updated: Sep 20 '12