Which transformation is associated with the use of four or more control points?

The projective transformation is particularly useful when working with four or more control points. This type of transformation establishes a more complex relationship between the points in the source and destination coordinate systems compared to simpler transformations. Specifically, it can model perspective effects and is required for accurately mapping points in a way that incorporates varying scales and angles.

Utilizing four control points allows for the calculation of a transformation matrix that can handle rotations, translations, and scaling, in addition to the perspective distortions that occur when points are not aligned along parallel lines. This flexibility makes projective transformations ideal for images subjected to perspective changes, such as photographs taken from different angles or distances, where depth plays a significant role.

In contrast, other transformation types, such as affine and polynomial transformations, have different requirements and functionalities. Affine transformations only require three points and are limited to transformations that maintain parallelism and do not involve perspective changes. First and second-order polynomial transformations are suited for different types of geometric adjustments but require specific arrangements of control points to generate their respective transformation matrices.