A camera imaging model with radial distortion

used for a structured light vision system to measure geometric tolerance

is introduced in this paper

together with an improved calibration of Direct Linear Transformation (DLT). First

with traditional calibration technique used on linear model

all the parameters can be worked out through solving super linear equations; second

with the results of first step as initial value

the inner parameters

such as Center Of Image

Equivalent Foci

Slope Factor

Coefficient Of Distortion

can be worked out through non linear iteration. Pre calibration is not necessary in calibration with this method. The method performs with suitable accuracy

and is proved to be simple and practical.