Darn, beaten by EnglishBob  :cursing:

Point at does not work well for billboards since they will tip if the camera moves up or down.

It can be done by script but its probably easier to adjust manually for a still image.for angle a

Plane geometry will give you the calculation for say (1,1) and camera at (9,7)  x and Z values.

 xstep is 8, zstep is 6 

so for angle a  x and z are opposite over adjacent = 6/8 = tan(a)

so atn(a) = 0.75 = 0. 643 radians = 0.643 * 180/pi = 36.8 degrees

 so rotate in Y to 36.8 to face the target.