[Plib-users] Problems using sgIsectPlanePlane(), point is always at 0, 0, 0

[Satz K. <sat...@go...>]

Hi,

 I want to find the intersection line out of two planes but fail
 miserably. That's what I'm doing:

 - I start with two triangles a1,b1,c1 and a2,b2,c2 that describe my
 planes and consist of three coordinates x,y and z for every corner of
 it
 - out of their corner coordinates x,y and z I calculate 3D vectors
 sgVec3 va1,vb1,vc1 by substracting the coordinate values b1-a1, c1-b1,
 a1-c1 and normalizing the result; the same is done for the second
 triangle's coordinates
 - then I call

 sgMakePlane (plane1,va1,vb1,vc1);
 sgMakePlane (plane2,va2,vb2,vc2);
 ret=sgIsectPlanePlane (point,dir,plane1,plane2 );

 But here the result is unusable and nearly every time the same.
 "point" always contains _very_ small values so that after rounding to
 6 decimal places the coordinates of it are 0,0,0.

 What am I doing wrong here?

 Elmi