Update heightmap size & added DEM example

[jennuine]

🦟 Bug fix

Requires gazebosim/gz-common#292

Summary

Updated heightmapSizeZ calculation, which was not ported from gazebo-classic. Thanks to @iche033.

Also updated heightmap example to include DEMs:

cd examples
mkdir build && cd build
cmake ../
make
./heightmap dem

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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[iche033]

nice demo works for me.

One suggestion is to keep the arguments to the heightmap example consistent with other examples, i.e.

./heightmap [engine_name] [graphics_api]

One idea would be to look for an --dem arg, e.g.

# I think your code will pick ogre 1.x by default - maybe useful to add a msg about this
./heightmap --dem

# same behavior as above
./heightmap ogre --dem

# tries to use ogre2 with dem
./heightmap ogre2 --dem

# tries to use ogre2 + metal with dem
./heightmap ogre2 metal --dem

[chapulina]

The demo works for me too. I like @iche033 's suggestions for the example's arguments.

[chapulina]

I've addressed mine and @iche033 's comments. I think this is good to go!

[chapulina]

@osrf-jenkins run tests please!

[chapulina]

Ahh, merging into #539 so we only iterate on CI in one place