Calculating Screen Space Error

Question

I'm currently working on a Level of detail system for an XNA game, the system subdivides triangles with high screen space error and merges triangles with low screen space error.

World Space Error is a heuristic which estimates the error that this triangle has, so for example if there is a triangle which is on an almost flat surface, it'll have a very low screen space error because it's a very good approximation of that surface, however if there is a triangle on the surface of a sphere it'll have a higher screen space error because obviously splitting that triangle up into more triangles would get a better approximation of a spherical surface.
Screen Space Error is a slight modification of World Space Error, basically the error is modified so triangles closer to the camera, and closer to the centre of the field of view have a higher error score.

What is a good and efficient way to calculate screen space error?

Current Solution: Screen Space Error = World Space Error / dot([vector to triangle in question], [camera direction vector])

Blog post about screen space error

Answer 1

You should check out these slides which explain screen space error in detail and derive formulae for calculating it. In particular, a simple method is given on page 3 (equation 1). Note that the rest of the pages detail improvements to this simple method, which might be of interest to you if you're trying to do something more advanced.