Add CesiumGeoreferencingInterop blueprint class.

[kring]

This is a PR into #1217 so merge that first.
Fixes #1169

Unreal Engine has its own GeoreferencingSystem, described here:
https://docs.unrealengine.com/5.1/en-US/georeferencing-a-level-in-unreal-engine/

It won't really work as a replacement for the CesiumGeoreference, but it still has two useful purposes in a Cesium app:

1. Because it ships with the engine, there's a pretty good chance various things in the Unreal ecosystem make use of it.
2. It has a lot more flexibility than CesiumGeoreference for specifying the location of the origin. Cesium only supports ECEF and WGS84 longitude/latitude/height, but GeoreferencingSystem can use any projected or geographic CRS that PROJ supports.

So, using both the CesiumGeoreference and GeoreferencingSystem in a single level is sometimes necessary or useful. And that leads to the awkward situation where both need to be kept in sync. For example, see this part of the Using Web APIs like Google Maps API from Unreal Engine (BP Only) tutorial:

We could solve this by teaching the CesiumGeoreference how to automatically synchronize with the GeoreferencingSystem. The problem with this is that it would require that the Cesium for Unreal plugin depend on the GeoReferencing plugin. In order to avoid that, I've taken an alternate approach in this PR. I've added a Blueprint class derived from CesiumGeoreference called CesiumGeoreferencingInterop. This acts just like a normal CesiumGeoreference, except it has some extra functionality:

Two Blueprint- and Editor-callable functions allow bidirectional syncing between this CesiumGeoreference instance and a selected GeoreferencingSystem. And there's also an option to automatically copy any CesiumGeoreference changes to the GeoreferencingSystem.

Adding an instance of this Blueprint class to your level with still require you to activate the GeoReferencing plugin. But Blueprint's late binding (compared to C++) allows us to ship this class with our plugin without taking a hard dependency on the other plugin.

I'm opening this as draft because I need to do some more cleanup and testing.

[cesium-concierge]

Thanks for the pull request @kring!

• ✔️ Signed CLA found.

Reviewers, don't forget to make sure that:

• Cesium for Unreal Samples works.

[kring]

When packaging a game that doesn't use the new CesiumGeoreferencingInterop Blueprint and also doesn't have the GeoReferencing plugin enabled, we get a bunch of scary messages in the log:

LogLinker: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: VerifyImport: Failed to find script package for import object 'Package /Script/GeoReferencing'
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  Georeferencing System  no longer exists on node  Get . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  <Unnamed>  no longer exists on node  K2 Engine to ECEF . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  <Unnamed>  no longer exists on node  K2 Engine to ECEF . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  Target  no longer exists on node  K2 Engine to ECEF . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  Engine Coordinates  no longer exists on node  K2 Engine to ECEF . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  ECEFCoordinates  no longer exists on node  K2 Engine to ECEF . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a function named "K2_EngineToECEF" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  K2 Engine to ECEF
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "OriginLongitude" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set OriginLongitude
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "OriginLatitude" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set OriginLatitude
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "OriginAltitude" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set OriginAltitude
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "PlanetShape" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set PlanetShape
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "bOriginLocationInProjectedCRS" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set bOriginLocationInProjectedCRS
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  <Unnamed>  no longer exists on node  Apply Settings . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  Target  no longer exists on node  Apply Settings . Please refresh node or break links to remove pin.
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a function named "ApplySettings" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Apply Settings
LogBlueprint: Warning: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] Could not find a variable named "GeographicCRS" in 'CesiumGeoreferencingInterop'.
Make sure 'CesiumGeoreferencingInterop' has been compiled for  Set GeographicCRS
LogBlueprint: Error: [AssetLog] C:\Program Files\Epic Games\UE_5.1\Engine\Plugins\Marketplace\CesiumForUnreal\Content\CesiumGeoreferencingInterop.uasset: [Compiler] In use pin  Georeferencing System  no longer exists on node  Get . Please refresh node or break links to remove pin.

However, it still packages and runs successfully.

[kring]

I wanted to try a thing or two to avoid those errors, but I can't seem to get them to happen again, no matter what I do. I reset the project to a clean checkout from the Samples repo. I deleted my DerivedDataCache. I deleted the plugin and re-extracted it from the ZIP. Still those errors won't come back. Very strange.

[kring]

I think possibly the reason I was seeing packaging errors initially is because I had an object in the project that referenced the CesiumGeoreferencingInterop class. It seems that engine plugin assets that are not referenced by the project at all are not included in the packaged game, which is great.

However, when the plugin exists in the project's Plugins directory (rather than in Engine/Plugins/Marketplace), then the asset does get compiled and included, even if nothing else in the project uses it. And if the GeoReferencing plugin isn't active, then the resulting compilation failure will stop the packaging from completing. It seems to be actually pretty common for people to put our plugin in their project directly, so it's really unfortunate that including this extra interop blueprint will break their projects. I can't really see a solution to this, so our options are:

1. Just change Cesium for Unreal to require the GeoReferencing plugin. Then the interop support can be in C++ and no special tricks are needed. But we end up with an extra dependency.
2. Provide the interop blueprint with the plugin, but don't put it in the Content directory. Instead, put it somewhere UE won't see it by default, like Extras. Users that want to use it can copy from there into their project. Biggest downside: once the user has copied it, we have no ability to update it for future versions.
3. Don't provide the interop Blueprint at all. Instead, just tell users how to create it themselves in some sort of tutorial or whatever.
4. Create a separate Blueprint-only plugin that depends on both CesiumForUnreal and GeoReferencing, and put the Blueprint there. We can publish it to the Marketplace. Because it can be Blueprint-only, we shouldn't need to update it for every UE version or even for every CesiumForUnreal version, so the maintenance burden should be relatively low.

I'm currently thinking that (4) is the best solution. In which case this doesn't need to be part of v2.0 because it won't require any changes to Cesium for Unreal at all.

[csciguy8]

2. Provide the interop blueprint with the plugin, but don't put it in the Content directory. Instead, put it somewhere UE won't see it by default, like Extras. Users that want to use it can copy from there into their project. Biggest downside: once the user has copied it, we have no ability to update it for future versions.

I like the idea of 2), maybe also 3), just from an aspect of effort. The few users who need this can try it out, assuming they don't already have some mechanism to solve this. For us, it doesn't bog down our development efforts in a significant way. It's almost an implied nudge to use one or the other completely.

[cesium-concierge]

Thanks again for your contribution @kring!

No one has commented on this pull request in 30 days. Maintainers, can you review, merge or close to keep things tidy?

I'm going to re-bump this in 30 days. If you'd like me to stop, just comment with @cesium-concierge stop. If you want me to start again, just delete the comment.

[gabrielamelian]

Hi there, I just wanted to check if there are any updates on this. We are doing quite a bit of work trying to implement means to sync UE Georeferencing, Cesium and ArcGIS plugin, and knowing whether this is going to be implemented or not might affect how we go about things.

[kring]

No, we're unlikely to merge this, because it requires dependencies that we don't want to take. My attempted workaround of that problem didn't actually work.

However, you can feel free to use the code in this PR in your own project if it helps you.