2d to 3d

Hi,

its a general 3d problem, i have a rectangular polygon, and its rendered on the screen. Any one tell me, in the rendered geometry on the screen howmch length a pixel curresponds to the real 3d space. I mean any specific formula for that..........?consider the polygon is at different depths in the 3d space..

It depends on your projection matrix, how do you set it up? The length in world space that corresponds to one pixel in screen space is directly proportional to the distance from the viewer in world space. I.e. a line twice as long at twice the distance will be the same length on screen.