DEM smoothing

[dbetchkal]

One issue with developing naive trajectory files from x,y points involves setting the appropriate z values. (In short: planes don't respect sudden dips in elevation from valleys or canyons.) A 90th percentile smooth of the raster allows more appropriate "above ground level" (AGL) estimations.

Two changes required:

• 1. Update NMSIM_Create_Base_Layers.py to also save a more typical elevation raster (as .tif)

• 2. Then simplify Convert ESRI shapefile (.shp) to NMSIM trajectory (.trj) to automatically smooth the .tif and compute altitudes AGL given only x, y positions. Enhance by allowing point-by-point override of altitude, but also velocity with column names from the .shp file.