# Revision history [back]

I'll write an answer to the issue after doing some experiments. I corrected my distance as follow:

Distance_corrected = distNorme+distNorme*correction


distNorme is the distance to the chessboard which is the norm of the translation vector given by solvePnP OpenCV function.

correction is

correction=pixel_size/focal_mm/2 = 2/focal_pixel


The results are better, still have an error increasing linearly though but not very strong as distNorme (distance not corrected).

I'm still seeking for references or documentation of that correction error. I need more details about it.