OneAxisEllisoid.projectToGround(TimeStampedPVCoordinates, Frame) fails if point is exactly on ground
Projecting a ground point to ground triggers an error when attempting to compute the zenith vector.
The error is due to zenith being computed by normalizing the vector from
ground point to original point.
When the point is already on ground, this vector is null and normalizing it fails.
(from redmine: issue id 181, created on 2014-11-24, closed on 2015-01-12)