1. The problem statement, all variables and given/known data I am working in Matlab, and have a 3D plot that I made: x is parallel to axis labeled "lateral direction (m)" y is parallel to axis labeled "long. dir. (m)" z is normal to these (right hand coordinate sytem) The original view was looking parallel with +y. To get the current view, I rotated our viewpoint about the x axis -15 degrees, then rotated about the ORIGINAL z axis 10 degrees. How do I calculate the angle that the x axis now forms on the page? For comparison, I used image editing software to measure the angle of the axis. It is a rectangle 12 high, 322 wide, so the angle is -2.134 deg. 2. Relevant equations 3. The attempt at a solution I attempted to do rotation matrices. I did: phi = -15deg theta = 10deg A = [cos(theta) sin(theta) 0; -sin(theta) cos(theta) 0; 0 0 1] B = [1 0 0; 0 cos(phi) -sin(phi); 0 sin(phi) cos(phi)] B*A = [ cos(theta), cos(phi)*sin(theta), -sin(phi)*sin(theta); [ -sin(theta), cos(phi)*cos(theta), -cos(theta)*sin(phi); [ 0, sin(phi), cos(phi)] And do get the angle that the original x axis forms with our new viewpoint, I do r = [1; 0; 0] then do: B*A*r and I get: [cos(theta); -sin(theta); 0] Which does not give me a correct result. Not only that, there is no way that a rotation in two different axes does not depend on both theta and phi.