With regard to the triangulation, you may want to look into the massive C/C++ library, Visual Toolkit (VTK). They also have wrappers for more friendly languages such as Python.

If you want the true angle between the vectors in 3D, you actually have two angles in spherical coordinates. Phi and Theta as functions of Cartestian:

Theta = r*arccos(z)

Phi = r*arctan(y/x)

Since you have unit vectors, r=1. Get Theta and Phi for each vector and then take the differences.

Alternatively, you can get the projected angle between the two vectors simply from the dot product:

u.v = |u|*|v|*cos(a)

I imagine there are more clever ways of doing this as well.

Thanks for your answers so far. I wish work on implement them. Please I will appreciate more contributions. Thanks once again.