As shown in Fig 1, the measured angle forms a right spherical triangle with the true azimuth and the elevation.
The angle from north to the velocity vector can be determined using the right spherical triangle formed by the velocity-vector azimuth and elevation angles.
The two right spherical triangles and one spherical triangle of Fig 5 allow the calculation of the angular distance from the roll axis and the target (j):
As shown in Figure 3, a right spherical triangle has one 90[degree] "angle.
Note that the five-segmented disk in Figure 4 includes all of the parts of the right spherical triangle, except the 90[degree] angle.