As no one seems to be able to offer help on this, let me try to clarify the problem:
Imagine a quadrilateral of paper PTSR is folded into two triangles along PS.
The quadrilateral/ triangle pair is sat on a plane on edges RS and ST.
The angle between the two planes of the triangles (the fold PS) is adjusted until PR and PT are in plan at right angles.
How can this condition be solved to get the unknown information e.g. h, RO, OT, angles ROT and SOT etc.?
I am only interested in solutions in the quadrant shown (with OT and OR positive) and with OP positive.
Help, please! Thanks, cadastralrob.