Cees,

I'm an engineer, too. Tested out of the electronics classes and most of my freshman year + some others along the way, double-majored in computer science (systems development, and scientific applications - mostly math), with a math minor (5 hours would have given a triple major - CS/Sys, CS/Sci, and Math). You are totally missing the point. There absolutely MUST be some distortion - geometrically impossible NOT to have some. Plus I graduated early.

To demonstrate it very easily, get yourself a tapered-wing airplane. Get yourself a camera with a 50-70mm lens. Get lots of light. Now, position yourself just outside one wingtip and 0.5m above it. Put the center of your focus on the wing where the fuselage would be (works great with the fuse there, too). CLICK.

Print it. Now measure the root, and both tips. Tell me there's no distortion. All the lines are straight, but your close tip will probably measure LARGER than its root.

Because you know your location, the lens, and the subject you can figure out exactly the distortion. Take another picture from above and behind the tail, centering on the canopy. Voila!

Then please post your pictures and measurements here.

Andy