DEM Files

DEM (Digital Elevation Model) files are exactly what they sound like: they hold elevation models.  These elevation models correspond to areas that have been mapped in a digital format for 3D reconstruction.  They usually have a .tif or .dem file extension (we use .tif files generally).

These are usually collected by the government or private corporations using LIDAR attached to planes.  These planes fly over the area, gathering the elevation of the terrain using LIDAR.  Lucky for us, many of these datasets are open to the public and published on sites like 

http://opentopography.org/ 

https://gis.utah.gov/data/elevation-and-terrain/

These sites usually contain a GUI or command line interface that allow you to download a DEM corresponding to the particular area that you are interested in.

For a great tutorial on DEM files, see http://gazebosim.org/tutorials?tut=dem .  However, note that for our project we do not import the .dem files directly in Gazebo, as they do not easily allow us to change its texture, or its orientation/rotation.  

In my experience, I would download a .dem file, and notice after importing them into Gazebo that its coordinate system was 90 degrees off from Gazebo's inherent system.  So north in Gazebo could be east in the heightmap. This was a problem because heightmaps cannot be rotated in Gazebo (as far as I could tell, and according to this site https://bitbucket.org/osrf/gazebo/issues/2167/not-possible-to-change-the-pose-of).

Once you have your dem file, you will need to get a Google Earth image corresponding to the same area.  It might be a good idea to follow the tutorial mentioned above, not to get a final project, but to visualize the area in Gazebo.  On the other hand, if you still have the GUI still open, you could use that to help "guesstimate" the area you need.  In my case, I simply used the snipping/screenshot tool to save a label-less Google Earth image of the area corresponding to the part of campus that I wanted to use.

From there, you are going to need blender.