What does the function anglesub do? Can you please post its code?
What do you mean with TrueAngle?
Is your 3d field in perspective?

What coordinate system are you using (Left hand or right hand?) and in what direction are the axises pointing.

I think more information is necessary in order to solve your problem.



Suppose, you're having no perspective and you're using a left hand coordinate system, and x is pointing out of the screen (towards the user, and for perspective purposes I'm letting it point towards lower left in an angle of about 30 degrees, actually atan(0.5)), y to the right and z to above, then you can draw a position like this:

TargetX = 320 + y - 0.5x
TargetY = 240 - z + 0.25x