Add functions to get the approximate location of a tileset during runtime

[arbertrary]

As discussed in the following Cesium community forum thread, there is no API-level support to get the world location of a tileset during runtime from UE blueprints.

https://community.cesium.com/t/get-coordinates-of-cesium3dtileset-spawned-at-unknown-location/33087/4

As suggested by @kring I had a look at the ACesium3DTileset::OnFocusEditorViewportOnThis() function.
With this pull request I added two functions that return an approximate location (Unreal and ECEF) of the tileset calculated using the rootTile.

Disclaimer:

• The code might not be in the most suitable locations, I simply lack the overview of the bigger picture of the Cesium for Unreal source code and where to place which kinds of functions
• I did not use the center of the bounding Box or Sphere to calculate the location. This is because for one of my own tilesets that I used to test this code with, this would always place me far above the tileset (thousands of meters)
• I think calling it "approximate" is necessary because otherwise this would probably fuel expectations that this code cannot fulfill 😄
• I was only able to test these functions anecdotally

[arbertrary]

If there is no root tile returned by this->_pTileset->getRootTile() this currently returns the Zerovector without warning which results in obviously incorrect coordinates.

I'm not sure what causes a tileset to not have a root tile but it seems to be the case for some tilesets.

ACesium3DTileset::OnFocusEditorViewportOnThis() also simply returns if it encounters a nonexisting root tile so I'm not sure how to best handle this here 🤔

[kring]

Thanks for the PR @arbertrary!

The root tile is part of the tileset.json, which is download when the tileset is first loaded. Until that download / parse completes, we don't know anything about the tileset, not even where it's located.

There's nothing for it other than to give the function a way to return "I don't know yet" as the answer.

[arbertrary]

I have added a warning and a boolean out value to the function so that this gets propagated and can be checked in blueprints.

Unfortunately this wasn't actually the problem. For some tilesets the function returns 0,0,0 even if the root tile is available. The !prootTile condition was actually never entered.

Tilesets where that was the case:

• Nearmap Boston Photogrammetry https://ion.cesium.com/assetdepot/354759
• New York City 3D Buildings https://ion.cesium.com/assetdepot/75343

Tilesets where the code does work for me as expected are for example

• Melbourne Photogrammetry https://ion.cesium.com/assetdepot/69380
• Montreal Pointcloud https://ion.cesium.com/assetdepot/28945

[arbertrary]

Unfortunately this wasn't actually the problem. For some tilesets the function returns 0,0,0 even if the root tile is available. The !prootTile condition was actually never entered.

Checking whether the initial load of the tileset is complete by confirming that LoadProgress equals 100.0 before calling getApproximateLocation doesn't change this as well.