Expose API to set non earth DEMs flag

[adityapande-1995]

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🎉 New feature

Summary

This PR exposes the isNonEarthDEM member so that it can be set before the Load function, if required.
Needed for this PR : gazebosim/gz-sim#1478

Test it

Added some lines to the existing Moon DEM load test case.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[ahcorde]

test?

[mjcarroll]

Was there a decision to revisit this variable naming?

[adityapande-1995]

Was there a decision to revisit this variable naming?

That was for using this flag later in Physics.cc, based on an sdf parameter which I had originally planned to be <non_earth_dem>, but which was decided to be changed to <surface_model> I'll change that here : gazebosim/gz-sim#1478.

For this PR, in the GetGeoRef call, we compare the transformations with the WGS84 earth model and only when that fails we can set the isNonEarthDEM flag. We cannot know which celestial body it belongs to, just that it is not from the earth :

gz-common/geospatial/src/Dem.cc

Line 290 in d5f1c97

targetCs.SetWellKnownGeogCS("WGS84");

. So we can change the sdf param to expose what celestial body a DEM belongs to, but for this use case we can only use the information whether the DEM is from the Earth or not.

For e.g. in this test, the GetGeoRef call fails in Load and sets the isNonEarthDEM flag :

gz-common/geospatial/src/Dem_TEST.cc

Lines 233 to 251 in 600670b

	auto path = common::testing::TestFile("data", "dem_moon.tif");
	EXPECT_EQ(dem.Load(path), 0);
	EXPECT_EQ(33, static_cast<int>(dem.Height()));
	EXPECT_EQ(33, static_cast<int>(dem.Width()));
	EXPECT_FLOAT_EQ(-212.29616f, dem.MinElevation());
	EXPECT_FLOAT_EQ(-205.44009f, dem.MaxElevation());
	// unable to determne world width/height of non earth DEM
	EXPECT_FLOAT_EQ(-1, dem.WorldHeight());
	EXPECT_FLOAT_EQ(-1, dem.WorldWidth());
	// unable to get coordinates in WGS84
	ignition::math::Angle latitude, longitude;
	EXPECT_FALSE(dem.GeoReferenceOrigin(latitude, longitude));
	// The Load() method in Dem.cc should set the
	// isNonEarthDEM flag.
	EXPECT_TRUE(dem.GetNonEarthDEM());

, and we cannot know what exact celestial body it belongs to, at least for now.