# Planar Perspective and Radial Transformation

The CogTransform2DPerspectiveAndRadial is a transformation object that describes both planar perspective and radial distortion. There is no single mathematical representation that describes both planar perspective and radial transformation. The CogTransform2DPerspectiveAndRadial works by performing each part of the transformation separately, in this order:

1. The planar perspective transformation. The Checkerboard calibration tool uses this part of the transformation to account for the planar perspective distortion, to account for the physical tile size that you specify, and to center the origin at the optical center of the image.
2. The radial transformation. The Checkerboard calibration tool use this part of the transformation to account for the radial distortion in the image.
3. A linear transformation (translation and scale only). The Checkerboard calibration tool uses this part of the transformation to reset the scale and origin information that was changed by the first step.

Note: The planar perspective transformation step also includes the degrees of freedom associated with a 2D linear transformation: translation, scale, and rotation.