Bearing when a Point P is above the ERM Surface (Ellipsoid)
This is an edge view of the tangent plane (purple dotted) and the normal plane (red) at A.
A and B are on the ERM surface (B is below the horizon).
The green and blue arrows represent the normals NA and NB, respectively.
This is the defining geometry for bearing angle.
In this case the normal plane is rotated to the point P.
A and B are on the ERM surface (B is below the horizon).
The green and blue arrows represent the normals NA and NB.
This does not define the same bearing angle.
Mathematical adjustments need to be made to compute bearing. This process is called reduction.