Line of sight intersection with oblate spheroid

`[`

computes
the latitude and longitude (`lat`

,`lon`

,`slantrange`

]
= lookAtSpheroid(`lat0`

,`lon0`

,`h0`

,`az`

,`tilt`

,`spheroid`

)`lat`

and `lon`

)
of the first point of intersection of the line-of-sight from a viewpoint
in space with the surface of an oblate spheroid. If the line-of-sight
does not intersect with the spheroid, `lat`

and `lon`

contain `NaN`

s.

`lat0`

and `lon0`

are
the geodetic coordinates of the viewpoint on the reference spheroid, `spheroid`

. `h0`

specifies
the geodetic height of the viewpoint in space above the spheroid.
The `az`

and `tilt`

arguments
specify the direction of the view (line-of-sight) as the azimuth angle,
measured clockwise from North, and a tilt angle. The following figure
illustrates these measurements.

The optional `slantrange`

output argument
returns the (3-D Euclidean) distance from the viewpoint to the intersection.
All angles are in degrees.