Specifications of Checkerboard (Calibration) for obtaining maximum accuracy in stereo reconstruction

1
votes

I have to reconstruct an object which will be placed around 1 meter to 1.5 meters away from the baseline of my stereo setup. The image captured by both cameras have high resolution (10 MP)

The accuracy with which I have to detect it's position is +/- 0.5mm, in all the three co-ordinate axes. (If you require more details, please let me know)

For these, what should the optimal specifications of my checkerboard (for calibration) be?

I only know that it should be an asymmetric board. It should be placed in the same distance range as the range where object is expected to be placed. Also, it should be oriented in all possible angles (making sure all corners are seen by both cameras)

What about:

  1. Number of squares horizontally and vertically? (also, on which side should the squares be more / even?)

  2. Dimension of each square on checkerboard?

  3. What effect does the baseline distance have on this?

Do these parameters of the checkerboard affect my accuracy in anyway? Are there any other parameters I need to consider for calibration?

I am using the MATLAB Stereo Calibrator App.

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matlabcamera-calibrationmatlab-cvststereo-3d3d-reconstruction
I think your question is a bit broad. It's much better if you provide a concrete example with code, images, all the parameters etc(hint: see mcve. There are too many unknowns in your question imho. – kkuilla

1 Answers

4
votes

I will try to answer as good as I can:

  1. Numbers of squares. Well, as you can guess, the more squares (actually corners between squares are used!) the better the result will be, as you have a more overdetermined system of equations to solve. Additionally, it doesnt matter the size of the chequerboard, only the odd/even pattern matters.
  2. Dimensions of squares. the size does not matter very much in "mathematical" reresentation, but it matters practically. If your squares are very small, probably your printer wont draw a that good corner of the square and that will make your data "noisier". In the past, for really small calibration system I needed to go to an specialised printing shop so they could print it with the maximum quality possible. Of course if you make them very big you wont be able to fit lost of them in the iage which is not good.
  3. The baseline distance has effect only in how properly can you see the corners between squares. The more accurate (in mm!, real distance!) you are detecting this corners the better. Obviously if you make small squares and put them very far, well, you wont see very much. This fits with the 1,2 question. Additionally, another problem you may have is focal length. In a application I worked on, some really small and close things wanted to be imaged. That was a problem while calibrating, as the amount if z distance I could see without blur was around 2mm. This really crippled my ability to calibrate properly because I could big angles in Z direction without getting blurred corners.

TL;DR: You want to have lots of corners between squares of the chequerboard but you want to see them as precisely as possible.