PLEASE HELP: estimating 3d orientation of object from single image (using 3 markers)

Dear *, I need to determine the position and orientation (in 3d) of a given object, but using only a single camera (i.e., a single picture).
to do so, i can put 3 markers on the object to track, so that the problem scales down to estimating the 3d position/orientation of a triangle (from a projected image of that triangle, and knowing the inter-point distances). But I don't have the formulas... Can you could help me out with the formulas (or maybe even a (pseudocode) program ? ;-) I would really appreciate it!!! Thanks in advance, Chris
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