A linear mapping method that preserves points, straight lines, and planes is called affine transformation. After affine transformation, sets of parallel lines will remain parallel. In general, the affine transformation technique is used in the correction of geometric distortions that occur with nonideal camera angles.
An example of affine transformation is as follows. Here, we are applying affine transformation to a rectangle, causing it to shear offsets—that is, a set of points that are moved a distance proportional to their axis:
Fig 4.53: Applying affine transformation to a rectangle
You can learn about affine transformation in more detail at https://en.wikipedia.org/wiki/Affine_transformation.
In the preceding diagram, we can see how a rectangle with four points changes after we apply affine transformation.
