If I have a velocity vector V in some coordinate system. Is there anything special that needs to be done to convert V -> V' ? Basically, I have a matrix (N x 3) in north-east-down coordinates. I am trying to convert (a row at a time_ to another matrix (N x 3) to earth-centered-earth-fixed coordinates. When I do the transformations with positions, it seems okay. When I do the transformation with velocity "positions" it seems messed up? Any ideas?