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# OpenGL GL_PROJECTION and GL_MODELVIEW matrices

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Hi all, I want to display some OpenGl cubes on top of an image taken by a camera. The equations to convert from world coord system(XYZ) to image coordinates(uv) are given below. How can I plug in the focal length(fx,fy) and principal point(cx,cy) into the OpenGL projection matrix? How do I have to set the GL_PROJECTION and GL_MODELVIEW matrices to obtain the same projection result as in the case of using the equations below? /******************************************** // Projection equations. // (R,T,fx,fy,cx,cy are know after a calibration step) double x = R[0]*X + R[1]*Y + R[2]*Z + T[0]; double y = R[3]*X + R[4]*Y + R[5]*Z + T[1]; double z = R[6]*X + R[7]*Y + R[8]*Z + T[2]; z = z ? 1./z : 1; x *= z; y *= z; int u = x*fx+cx; int v = y*fy+cy; Thanks

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Quote:
 double x = R[0]*X + R[1]*Y + R[2]*Z + T[0];double y = R[3]*X + R[4]*Y + R[5]*Z + T[1];double z = R[6]*X + R[7]*Y + R[8]*Z + T[2];

The above easily fits into a modelview matrix.
R[0], R[1], R[2], T[0]
R[3], R[4], R[5], T[1]
R[6], R[7], R[8], T[2]
0, 0, 0, 1

Quote:
 z = z ? 1./z : 1;x *= z; y *= z;int u = x*fx+cx;int v = y*fy+cy;

I think
1, 0, 0, 0
0, 1, 0, 0
0, 0, 1, 0
0, 0, -1, 0

will do the first 2 lines. I don't know about the last 2.
Is u and v suppose to be screen space?
The GL viewport works in a different way.
Have you considered writing a vertex shader.

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