DEM improvements to nodata, buffer and other corner cases

[chapulina]

🦟 Bug fix

Summary

Various small fixes to work with some DEMs I have:

Buffer to min height

Set buffer height to minimum height value. Non-square DEMs are automatically padded to become a square. The original logic is using height == 0 for the padding, which is very awkward for DEMs below ground. This PR changes the bufferVal to match the minimum height on the heightmap because a cliff down should be better than a cliff up, which is visible from far away.

Example:

Before (cliff up)	After (cliff down)

nodata comparisons

• All comparisons to NaN return false, which caused the if (d > noDataValue) check to prevent calculating the min / max values. I fixed that by guarding explicitly for NaNs.
• Another assumption in the current code is that the nodata value is smaller than all heights on the DEM. That's not the case for some DEMs I have here, which have very high values for nodata. So instead of checking if (d > noDataValue) I'm doing math::equal(d, noDataValue).

Dem::LoadData indentation

The entire function was too indented, so I fixed that as part of this PR. I recommend hiding whitespace changes to see what's actually changed.

GetProjectionRef and GetGeoTransform

These calls were returning values for my DEMs which weren't being well-handled. I added a guard and reduced an error to a debug message because the DEMs still work without these.

NetCDF

I also went ahead and used a NetCDF file (.nc) in a test to make sure we keep supporting this format.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

Merging #321 (ddd8add) into main (c06cbb6) will increase coverage by 0.00%.
The diff coverage is 82.97%.

❗ Current head ddd8add differs from pull request most recent head 921af7c. Consider uploading reports for the commit 921af7c to get more accurate results

@@           Coverage Diff           @@
##             main     #321   +/-   ##
=======================================
  Coverage   77.12%   77.13%           
=======================================
  Files          76       76           
  Lines       10528    10540   +12     
=======================================
+ Hits         8120     8130   +10     
- Misses       2408     2410    +2     

Impacted Files	Coverage Δ
geospatial/src/Dem.cc	90.99% <82.97%> (-0.47%)	⬇️

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[mjcarroll]

One place for const, LGTM.