# Checkerboard-based Hand-eye Calibration

Checkerboard-based hand-eye calibration involves using a calibration target with a Cognex checkerboard calibration pattern. This pattern contains either an L-Shaped Fiducial, or a set of DataMatrix codes that defines the Plate2D coordinate system the pattern. During hand-eye calibration AlignPlus can locate the corners of pattern in the image and identify their corresponding location Plate2D coordinate system. This correspondence is used to compute the hand-eye calibration results. The advantage of using the checkerboard are

- Each image contains a dense set of features. Therefore, as compared to part-based hand-eye calibration the motion device can move to fewer locations to get a reliable calibration
- If care is taken to ensure that the image of the checkerboard spans the entire field of view of the camera, an accurate estimate of lens and perspective distortion can be obtained
- The user does not have to add any feature finders to extract features in the image. AlignPlus extracts the features from the calibration target
- If an accurate checkerboard is used, the good quality of the calibration, and hence alignment can be obtained even if the motion device suffers from scaling and skew in its linear degrees of freedom

The disadvantages of using a checkerboard as a calibration target are as follows

- On some alignment systems, a special fixture may have to be designed to hold the calibration target. This is because the calibration target should be parallel to the plane of motion of the motion device
- The user would have to take care of the target and ensure that it is not damaged or lost
- Change to light settings, or additional lighting might be necessary to illuminate the calibration target