Hello,
You are correct, this function is not supported in Formula Nodes, and there is not a way to call VIs from formula nodes. However, the below solution might be what you need:
Is this the correct definition of atan2:
if y = atan2(a,b), then tan(y) = (a/b)
If so, could we define a and b, and use the formula node function atan(a/b)? This may not be the most elegant solution, but it seems like it would do the trick with minimal headache. I attached a VI showing this idea.
Hope this helps!
Liz Fausak
National Instruments