Maybe, you are the expert to answer this:
I want to turn a model's tilt and roll depending the normal of the surface traced beneath it. For a long while, I thought this is easily done by vec_to_angle:

c_trace(my.x, vector(my.x,my.y,my.z-1000), IGNORE_ME|IGNORE_PASSABLE);
vec_to_angle(temp, normal);

But, it obviously is not.

What's your advice?