get normal associated to point

I was wondering how it would be possible to get the normal associated to point determined such as in the FlightsDemo. In this demo, a method called "findnearestpoint" is used.
I don't know how this method works, but it would be very useful (at least for me) to know the normal at this point.

Thank you in advance for help.

The Viewport3D.FindHits extension method in this library returns HitResults that contains normal vectors!