Like what was said previously, the trig is not going to be a problem instead its the vision proc.
The triangulation tracking won't take much more processing then 2 *(current load for 1 camera + pointing).
However, a 3d disparity map for stereo optics will take the load of the previous as well as the load of the calculations to make the map and then find a target and distance.
Here is a whitepaper on stereo optics
http://www.cse.unr.edu/~bebis/CS791E...ereoCamera.pdf