Adds valid height check for DEM intersection

[jlaura]

Licensing

This project is mostly composed of free and unencumbered software released into the public domain, and we are unlikely to accept contributions that are not also released into the public domain. Somewhere near the top of each file should have these words:

This work is free and unencumbered software released into the public domain. In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain.

• [x] I dedicate any and all copyright interest in this software to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

[jlaura]

@acpaquette I just realized that this repo has not testing CI 😨!! This PR is passing locally (with warnings related to the PVL library). How do you want to proceed? I don't want this to become an uber PR. I can open another PR with testing setup, we can get that merged, and then re-review/re-run this one. Or you could pull this PR local, also verify that it is passing and then we can get an issue open.

I did not mean for this to become a thing!