Constructs a ModOp, that transforms the Src points to the Dst points. The length of Src and Dst must be equal and less than 5. If the length is 1, the resulting ModOp is a translation, if the length is 2, the parameter DoScale decides whether the resulting ModOp is a translation and rotation (DoScale==false) or translation, rotation and scaling (DoScale==true). If the length is 3 or 4, the resulting ModOp is any kind of an affinity, that projects the src points to the dst points.