# Specifying an Affine Rectangle and Sampling Parameters

You can specify the projection region as an affine rectangle and affine rectangle sampling parameters. The projection direction is defined as being parallel to the Po-Py side of the affine rectangle, and the number of Po-Px divisions specified by the affine sampling parameters defines the number of samples in the projection region.

The following figure shows how an affine rectangle and affine rectangle sampling parameters determine the projection region: