Support DEMs

[caguero]

Once heightmap support is ready, we should add support to load a Digital Elevation Map. When loaded, we need to provide a basic API to query the main properties of the DEM, and then, load it as a heightmap.

[chapulina]

Here's the latest series of PRs:

• Geospatial component for heightmaps (2nd try) gz-common#292
• Require geospatial component gz-rendering#539
• Update heightmap size & added DEM example gz-rendering#560
• Added DEM support to heightmaps gz-physics#315
• Added DEM support #1262

[jennuine]

All PRs are merged.

[Ryanf55]

Quick question, is there any documentation or tutorials on how to use this feature? I was unable to find any.

[jennuine]

Unfortunately, the only tutorial available is from gazebo-classic found here: https://classic.gazebosim.org/tutorials?tut=dem&cat=build_world

It is outdated but will hopefully get you in the right direction. When following the tutorial, you should be able to copy this section into a Gazebo Garden compatible SDF world: https://github.com/gazebosim/gazebo-classic/blob/1bef2dc573aa15ca8a56b4a7dadb9905cf978582/worlds/heightmap_dem.world#L8-L54

If you'd like to contribute, feel free to open a PR for a newer tutorial on DEMs here: https://github.com/gazebosim/docs 😄