I think if you look at:

http://www.povray.org/documentation/view/3.7.1/246/

you'll see several things.

1. The +/- 0.5 range for x and y

2. camera angle is determined by changing the length of the direction vector.

3. I think this relates to the error you see, and it's decrease with smaller
camera angles.

Here's my crappy reasoning-by-analogy in the absence of the code in front of me,
and on short notice:

When you swivel a line through pivot point, a small change at the end results in
a large change in the other end when the pivot point is close ( small direction
vector / wide angle)

When you pull the camera way back, you have to make very large changes in the
position to have the same effect - or put the other way - any changes at the
other end are very small (your errors) for the same amount of change.

Think about that in terms of any trace() results and calculations based on those
- they're like angles, and like levers they can magnify (by integers or
fractions) the results.



I don't think you're/we're going to get very far fiddling with code or working
backwards from the existing macro.

Write some code to model a default camera scene, and then play with point
locations and their projection onto the z=1 plane.

Then you can work from there.

What you do (and understand) in a forward, stepwise manner, you can follow
stepwise, backwards to see what calculations you need to to go from screen
coordinates to 3D vector coordinates.

Post a reply to this message