DEM of Portuguese Ledge

[caguero]

Create a 5x5 km Digital Elevation Model (DEM) of Portuguese Ledge in Ignition from MBARI high-precision octree maps of the area’s bathymetry.

[chapulina]

This is a work in progress. PRs and branches I'm working with:

• https://github.com/ignitionrobotics/ign-common/pull/321
• https://github.com/ignitionrobotics/ign-physics/pull/315
• https://github.com/ignitionrobotics/ign-rendering/pull/585
• https://github.com/ignitionrobotics/ign-gazebo/pull/1262

Notes about manipulating the raw files:

• ign-common is able to load NetCDF directly
• The NaN notada values are causing trouble.
  • I used QGIS's "Fill nodata" tool with 10000 px distance and was able to load the file (which ends up being GeoTIFF)
• Loading the entire DEM consumes a lot of memory, it may be more interesting to split it and use levels
  • Saving the cached DEM can take up to a minute and freezes the simulator. It would be interesting to delegate that to a thread.
• ign-common pads non-square DEMs so they become square, and the padding is ending up above ground for this specific file
• I haven't checked whether lat/lon look reasonable after loading the file yet