   Finding the axis of rotation
  I have two vectors representing the normals of two faces one on each of two objects. I want to rotate the fisrt object by x degrees/radians where x is the angle between these two vectors. To rotate the object I need not only the angle in radians but the axis about which to rotate the object. Originally I had been using the cross product to calculate the axis which works perfectly in every situation but one. If there are 180 degrees between the two normals [ie they are parallel] then the cross product is 0,0,0Any idea how else I could get the axis vector or compensate for this one issue?   Planetblaze.com - http://www.planetblaze.com - As METAL as it gets! 
  If there are 180 degrees between the vectors then you can use any rotation axis that lies on the plane defined by the normal of either of the vectors.so say you've got vector A and vector B...do A cross (1,0,0) and normalise it and use it as the rotation axis... if the cross product of A and (1,0,0) is (0,0,0) then take the cross of A and (0,1,0) instead... its a bit messy but it works.   [edited by - SpaceDude on February 3, 2004 4:12:52 PM];  Ah I was so close to getting that myself  Thanks for your help 