void glOrtho( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble near_val,
GLdouble far_val )
near_val and far_val are distances from Z=0, along the negative Z axis
void gluPerspective( GLdouble fovy,
GLdouble aspect,
GLdouble zNear,
GLdouble zFar )
fovy = field of view, in Y direction
The "eye-point" of the perspective projection is at (0,0,0)