# DataMatrix Fiducial Marks

In addition to the simple 'L'-shaped origin fiducial mark, the Checkerboard Calibration tool also supports calibration plates with multiple DataMatrix code fiducial marks. These plates use DataMatrix codes to label the locations multiple grid vertices on the plate as well as the plate's grid pitch (the distance between successive corresponding points or lines). The following figure shows how multiple DataMatrix fiducial marks serve to label four vertices on a checkerboard calibration plate (in this case, a plate with a 2mm grid pitch):

Note: All Cognex-supplied DataMatrix plates encode the grid pitch; plates that you construct using Cognex-supplied CAD data may not include the grid pitch.

The handedness and orientation of the plate coordinate space are defined by the orientation of the DataMatrix mark, as shown below. The postive X- and Y-axis directions are established by the orientation of the finder pattern.

If the plate is mirrored (as would be the case if a transparent plate were viewed from behind), the calibration tool detects that the DataMatrix symbol is mirrored, and inverts the handedness of the coordinate system.

Checkerboard calibration plates with DataMatrix fiducial marks provide several important advantages:

- The plates enable the use of the CheckerboardExhaustiveMultiRegion mode in standard 2D camera calibration. This permits calibration in cases where reflections or other occlusions hide regions of plate vertices. Using this mode, the calibration tool can make use of multiple regions of vertices, as long as each region contains at least one fiducial mark.
- The plates enable the use of the ExhaustiveMultiRegion mode in 3D camera calibration. This greatly improves the accuracy and robustness of 3D calibration.
- The plates make it possible to use the CogHandEyeCalibrator with multiple cameras with non-overlapping fields of view, as long as each camera can see at least one fiducial mark from the same plate at the same time.

Note: Cognex does not publish the specific encoding used for DataMatrix fiducial marks. Cognex can provide high-accuracy DataMatrix fiducial plates in a wide range of sizes, grid pitches, and materials. Contact your Cognex representative for more information.