# Vision Toolbox Question: Is there a way to access the z-coordinate from the camera calibration process?

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Thomas Stepan el 2 de Mzo. de 2016
Respondida: Thomas Stepan el 2 de Mzo. de 2016
Is there a way to access the z-coordinate from the camera calibration process? I wish to perform 3D vector math between calibration planes (i.e., the checkerboard planes shown when using showExtrinsics with plotCamera). The Calibration App shows a 3D plot of all the calibration checkerboards relative to the camera frame of reference (i.e., relative to the camera origin x,y,z = 0,0,0). Clearly, the Calibration App uses a z-coordinate to produce the plot. I would like to access the z-coordinate if available, or calculate it. Thanks for help with this question.
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Dima Lisin el 2 de Mzo. de 2016
Hi Thomas,
In the checkerboard's coordinate system the points on the checkerboard all have z=0. If you want the checkerboard points in the camera's coordinate system, then you have to transform them. Let [Xb, Yb, 0] be a point on the checkerboard in the checkerboard's coordinates. The same point in the camera's coordinates would be
[Xc, Yc, Zc] = [Xb, Yb, 0] * R + t
where R and t are the extrinsics associated with that checkerboard. Note that we are using row vectors here.
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### Más respuestas (1)

Thomas Stepan el 2 de Mzo. de 2016
Hello Dima and thank you for the helpful reply to my question.
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