Discontinuity in gluLookAt

Question

This is how I calculate my line of sight vector and the up vector.

    ly = sin(inclination);
    lx = cos(inclination)*sin(azimuth);
    lz = cos(inclination)*cos(azimuth);
    uy = sin(inclination + M_PI / 2.0);
    ux = cos(inclination + M_PI / 2.0)*sin(azimuth + M_PI);
    uz = cos(inclination + M_PI / 2.0)*cos(azimuth + M_PI);

inclination is the angle of the line of sight vector from the xz plane and azimuth is the angle in the xz plane.

This works fine till my inclination reaches 225 degrees. At that point there is a discontinuity in the rotation for some reason. (Note By 225 degrees, I mean its past the upside-down point)

Any ideas as to why this is so?

EDIT: Never mind, figured it out. The azimuth does not need a 180 deg. tilt for the up vector.

Answer 1

I think you are talking of a limit angle of 90 degrees (pi). What you get is a normal behavior. When using gluLookAt, you specify an 'up' vector, used to determine the roll of the camera. In the special case where you are looking upside down, the 'up' vector is parallel to the eye direction vector, so it is not possible to determine the roll of the camera (this problem as an infinite number of solutions, so an arbitrary one is chosen by gluLookAt). May be you should compute this 'up' vector using your inclination and azimuth.