When I translate and rotate to a local coordinate system, how do i find the local coordinates of a point in global coordinates. In other words, I know the global coordinates for a vertex, then I move to a local coordinate system, how would I find the coordinates of the vertex with respect to the new local coordinate system?

# local/global coordinate system problem

Get the matrix that does the translations and multiply your vertex by it.

Chris

so, you mean use

`glGetFloatv(GL_MODELVIEW_MATRIX,Minv);`

to store the system into Minv and then do something like this?:

`void VMatMult(GLmatrix16f M, GLvector4f v) { GLfloat res[4]; res[0]=M[ 0]*v[0]+M[ 4]*v[1]+M[ 8]*v[2]+M[12]*v[3]; res[1]=M[ 1]*v[0]+M[ 5]*v[1]+M[ 9]*v[2]+M[13]*v[3]; res[2]=M[ 2]*v[0]+M[ 6]*v[1]+M[10]*v[2]+M[14]*v[3]; res[3]=M[ 3]*v[0]+M[ 7]*v[1]+M[11]*v[2]+M[15]*v[3]; v[0]=res[0]; v[1]=res[1]; v[2]=res[2]; v[3]=res[3]; }`

I think that’s right - I’m never quite sure what order GL’s matrices are in but I think you’ve got it.

Chris

Look at the other topic on matrix, I think we cover it pretty well now, it is over 70 replies now.

I stopped following when it hit 50

Chris