Ho do I calculate the angle between two 3d triangles?

Is it possible to compute angle between two 3d triangles always sharing two vertices?

Let's assume triangle1 consists of three points

P1=(x1,y1,z1), P2=(x2,y2,z2), and P3=(x3,y3,z3).

Triangle2 consists of the following three points

P1=(x1,y1,z1), P2=(x2,y2,z2), and P3=(x4,y4,z4).

Answer 1

[Bruno Luong]

P1=randn(3,1)
P2=randn(3,1)
P3=randn(3,1)
P4=randn(3,1)

E=P1-P2 % edge
Q = null(E')
v1 = Q'*(P3-P1)
v2 = Q'*(P4-P1)
theta1 = atan2(v1(2),v1(1))
theta2 = atan2(v2(2),v2(1))
theta = mod(theta1-theta2,2*pi) % radian

% Bruno

Note that there is always an ambiguity of the sign of the angle when working on 3D,

Answer 2

[Sean de Wolski]

Your problem looks very similar (i.e. identical) to this one:

http://stackoverflow.com/questions/2142552/calculate-the-degree-between-two-triangles-in-ansi-c-cuda

[konak]

yes, indeed, know i wanted to check whether what i get is similar to what i would obtain using matlab. thanks a lot!