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# 3d calibration

Hi ! I'm using the sample project for the 3d calibration, my question is about the input file the XML file. I don'T understand what I should but square size , is it the size in millimeter ? and what do they by metric system ?

!-- The size of a square in some user defined metric system (pixel, millimeter)--> <square_size> I should give her e the value !!!</square_size>

thanks in advance for help

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## 3 answers

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The square size is in whatever units you want to use. A good choice might be cm. Measuring accurately will allow you to make use of your calibration data by allowing you to determine the absolute coordinates of points and objects in such methods as Block Matching, Semi-Global Block Matching, and solvePnP. Also, understand that you need not recompute the distortion coefficients at different image sizes, but that you MUST scale your f_x, f_y, c_x, and c_y to the size of the image in question if it is different from the calibration image size. Some contend that it is good practice to obtain your calibration coefficients at various image sizes and appropriately average/combine the results.

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Hi!

I'm not sure about this, since I'm new myself to opencv, but I actually measure one chessboard square and place the value in there.

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I am guessing that you have to measure the square in mm.

( 2013-04-12 06:11:35 -0500 )edit

Hi, a have a big question, if square size is dimensionless ( i found a lot of document who confirmed that) why, if i put SS= 10000 or SS=1 i have totally different results in terms of intrinsic parameters?? I thought that should change only exstrinsic's one, but i have different Fx and Fy and in particolar way i have Cx and Cy very very close to ideal central point. Can yoy explain me that?

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Asked: 2013-04-11 05:27:48 -0500

Seen: 409 times

Last updated: Jul 17 '15