   Problems Extracting Frustum Planes in OpenGL [Solved]
  So I'm having some problems extracting the frustum planes in OpenGL.  I've found many references as to how to do this, such as these two linksExtraction of Frustum Planes - RavenSoftExtraction of Frustum Planes - LightHouse3DSo for the life of me, and please point out what I'm doing wrong, I can't get these equations to actually come up with the correct answer.Heres an example of a projection matrix in question.  First, lets work in viewspace, so the modelview is the identity.  And now lets use the gluPerspective(..) function to set up a frustum.A simple frustum is constructed with the call gluPerspective(90.0f, 1.0f, 1.0f, 10.0f) -- which means a square-shaped near plane at 1.0f, a far plane at 10.0f, and the right,left,bottom,top are all 1 unit away from the -z axis.The resulting OpenGL projection matrix from this call is1.000  0.000  0.000  0.0000.000  1.000  0.000  0.0000.000  0.000 -1.222  -0.2220.000  0.000 -1.000  0.000Now lets just determine the 'left' plane equation of the frustum, using the equation given from the two links provided.  They use the Ax + By + Cz + D plane equation, and the values are thus.A = m[0] + m[3];  // 1 + 0 = 1B = m[4] + m[7];  // 0 + 0 = 0C = m[8] + m[11]; // 0 + -0.222 = -0.222D = m[12]+ m[15]; // 0 + 0 = 0So heres my immediate problem with this.  The vector (1.0, 0.0, -0.222) will not represent the correct normal for the left plane.  Given that I've constructed a 90 degree frustum, the normal of the plane should be (1.0, 0.0, -1.0)(unnormalized) - but it is not.  So my question is, am I using the correct projection matrix to begin with? Should it not be straight from OpenGL?[Edited by - Gluc0se on August 18, 2006 5:27:18 PM]
  Double-check element 11; the matrix itself is right but you're using the wrong value in your manual computations.   ;  It appears to me that I have a tranposing problem, since it seems to work out ok if I transpose the matrix.  Though that printed matrix is already the tranpose of what is returned from OpenGL, meh I'm sure I just wasn't paying attention to the matrix ordering.  Thanks for the help   