> Does somebody can explain me what the operators * and / do exactly?
Scaling and rotation. Addition/subtraction does translation.
> for example
> select '(1,1)'::point * '(2,2)':: point ;
> gives
> (0,4)
This is analogous to complex arithmetic, where there are two orthogonal
dimensions. If you multiply '(1,1)'::point by '(2,0)'::point, then it
appears to be simple scaling. If you multiply by '(0,1)'::point instead,
then it is a rotation, flipping the input about the X axis.
hth
- Thomas