web cam calibrate

Question

I have 2 logistic webcam, I want to do stereo triangulation for which I have to measure the focal length of 2 web cameras.

My question is if I use openCv to calibrate the camera and generate the intrinsic and extrinsic matrices can I use the focal length value that is generated in the intrinsic matrix as the exact value of focal length.

Well in short i wanted to know if I can use 2 webcams to do stereo triangulation rather than using pin whole stereo camera...

That's the general idea, but real-world cameras are never going to match exactly the pinhole camera model, so the concept of "focal length" only holds up to some degree anyway... — Samuel Audet, May 03 '12 at 08:16
can you tell me how can i get the focal length from the yml fle? — MMH, May 07 '12 at 08:32
We can read it using the `CvFileStorage` functions of OpenCV, read the reference manual! — Samuel Audet, May 10 '12 at 13:19

score 2 · Accepted Answer · answered May 03 '12 at 09:18

Well, the answer depends on what you mean by the exact value of focal length. If the accuracy of triangulation is your concern then you need to know there are a few factors that affect the accuracy of calibration and triangulation. The rule of thumb is to have a wider baseline (the distance between the two cameras) to improve the accuracy of calibration. Second a larger number of points and more accurate points should be used for calibration. Third, check out the the back projection error after running bundle adjustment. Four, when triangulating the points further from the cameras have a larger uncertainty. And finally, apart from the first points, the wide baseline, the relative pose between the two camera is very important as you should consider what points you want to triangulate and relatively where in the 3D space they should be, then you can reconstruct some points that are important to you more accurate than the others. If you provide more details about the problem you're dealing with perhaps you get a more detailed answer too. I hope that helps.

can you please expalin hw could I get the distance between two cameras more accurately with the translation matrix.thanks — MMH, Apr 02 '13 at 06:36

web cam calibrate

1 Answers1