Compute the focal length of the projector (texture lighting)

I want to simulate the structured light technique, which uses a camera-projector pair to reconstruct a 3D scene. Thus I need to know the focal length of the projector besides some other parameters.

I’ve found a way to estimate all the params of camera, which can be found…blender-camera

But I have a hard time computing the focal length of the projector. I’m using the textured lighting as the projector, the projector has the resolution of 1024x768. I attached my blender file below, any help or insights would be appreciated.

sl_calib.blend (915 KB)