Hey David,

I think your approach is correct.

Based on the number rays vs the number of surfaces, you can use a different method.  You can use the CreateDirectUnpol if you have only a few surfaces but thousands of rays or you can use SingleRayDirectUnpol if you have dozens of surfaces but only a few rays.  Either way, I think you’ll have to use a loop outside the IBatchRayTrace interface to loop through either the surfaces or the rays.  If you’re using compiled code, these loops should not rally even be noticeable to the end user.

Something to keep in mind is this Cartesian distance approach will only work for homogeneous materials.  There is not really an efficient way to calculate the path length in a GRIN material.

If you just need total OPL and you don’t care about the OPL at each surface, you can create a function that converts from direct to normalized coordinates (the opposite of GetDirectFieldCoordinates) and run a CreateNormUnpol method & OPDMode.  Since a direct raytrace ignores ray aiming anyways, turning off Ray Aiming and using the paraxial entrance pupil for the Px/Py might be an easier task than looping through the CreateDirectUnpol method for each surface.