[Qgis-developer] Meaning of Georeferncer transformation types

[Zirneklitis]

Hi,

Please correct if I'm wrong.

The formulae for the Affine transformation can be expressed as follows:

Xc = r5 + Xp * r1 + Yp * r3
Yc = r6 + Xp * r2 + Yp * r4

(Xc, Yc - new coordinates;
Xp, Yp - pixel location;
r1 .. r6 - coefficients.)

In Quantum GIS Georeferencer the meaning of different transformations 
are as follows:

Linear - special case of Affine transformation where r3 = 0 and r2 = 0.

Helmert - special case of Affine transformation where r3 == r2.

Polynominal 1 == Affine transformation.

Thank You for Your time.
Karlis