Distance, point - environment

Is there a way to determine / compute the distance between a point and point in the model.
I want to know the Z-coordinate relative to the ground.
e.g. I have a point and want to know the distance to the ground(a model file)

                             | h
      |-------|      /
-----'         |----/     

( i want to dermine h )
Thanks for advice, hints, sollutions, …

if the point is going to be any arbitrary point above the ground, I would use a collision ray that has an origin at that point and collides with the geometry (or simpler collision surface) of the ground. You can then subtract one point from another to get your Vec3, and use the information of that vector how you wish (length() to get the magnitude or getZ() for the z component)