I'm trying to get the Hydra to act like a lightgun and want to put the mouse cursor where the hydra is facing on the screen, but with freepie I can just set the deltax/y.
I'm didn't read into python and its librarys, but it seems that I can't find a easy solution to do that.

You could easily use Hydra in mouse mode to APPROXIMATE this. However, since there is no calibration between the Hydra and your screen distance, the chance that the Hydra would exactly line up with the cursor, and stay there if you moved around, forwards/backwards, etc, is pretty non existent.

Do you really need the Hydra to 'point' at the cursor, or do you just want absolute mouse control by moving the Hydra around within a box sized area?

I want to calculate the intersectingpoint from the pointingdirection of the hydra with the screen.
I have the screendimensions and the position relative to the base station.

I-x--------I Screen
....\
.....\ O Base
......\
.......\\ Hydra

Huh, you can do absolute mouse position in Java with the awt.robot library...But I don't know if you can get FreePIE to interface like that.