Hi. Not really connected to ENIGMA, but still thought I might ask here. In one of my projects I need to transform from a convex quadrilateral to a rectangle. I though of just using bilinear interpolation, but got stuck at some basic ideas - mainly that the points for the convex quadrilateral with the point P has the origin still at the top left and so x0,y0 isn't 0,0 as it is in rectangle case. Here is a picture:

(note x0,y0, x1,y1... and so on are of course different for both the quadrilateral and the rectangle, I just named them the same)

As the transformation would be linear then the math isn't that hard, but I am tired now and if someone can figure it out in the next few hours while I am away, then that person gets a cookie (a virtual one).