Calibration grid distances

[PJFry]

Hello,

I have a camera with a fixed focal length and I am using a point grid for calibration.

I put the point grid at a distance of 1m from the camera (to fill the whole field of view with points) and point the camera perpendicular to the grid.

Will the calibration I get from that be valid for objects at other distances (like 0,3m or 5m from the camera) or do I have to take a calibration image for each distance?

Thanks in advance!

Philip

[BruceAmmons]

The scaling depends on distance, so the calibration is only good at the distance you have the calibration grid at.

Depending on how accurate you need the calibration to be, you could probably use some equations to determine the scaling at other distances.  Probably easier just to redo the calibration at the distance of interest, though.

Bruce

[PJFry]

Hi Bruce,

thanks for your answer. 

So far I have never really used the scaling, in calibration training I just leave the distance between the points as an arbitrary number. Later I do an additional correction which maps real world distances to pixel distances.

So without scaling, can I use the one calibration grid image from a fixed distance to correct the camera at different distances just for the distortion from the objective lens?

Do you know some literature that talks in detail about this, other than the NI manual?

Thanks,

Philip

[BruceAmmons]

If you are just looking at removing distortion and are not worried about scaling, it seems like it would work well.  You could always test it to be sure.

Bruce