Transformation determines method of converting your picture into map. This is done in MapTiler during georeferencing stage after at least three control points are set.
The most suitable transformation method is set automatically. However, you can always change this setting manually by clicking on gear icon in Georeferencer.
There are five transformation methods available. They differ in method of transforming your image as well as in minimal number of assigned control points:
Scaled transformation combines rotation, scaling, and translation. It doesn’t change angles and shapes and also preserves parallels.
It requires a minimum of two control points to be set in a line.
Similarity transformation combines rotation, scaling, translation, and reflection. It doesn’t change angles and shapes and preserves parallels.
It also requires a minimum of two control points, but they don’t have to be set in a line.
Affine transformation is any transformation that preserves collinearity and ratios of distances.
It is a linear transformation that needs at least three control points.
Polynomial transformation creates a polynom, that crosses all of the control points.
TPS transformation operates in three dimensions.
It requires multiple control points.