Add support for ellipsoid tileset loader

CHANGES.md

@@ -1,5 +1,11 @@
 # Change Log
 
+## Not Released Yet
+
+##### Additions :tada:
+
+- Added a "From Ellipsoid" option to `Cesium3DTileset` to generate a tileset by tesselating the surface of the ellipsoid, producing a simple globe tileset without terrain features.
+
 ## v1.13.1 - 2024-11-01
 
 ##### Fixes :wrench:
@@ -116,7 +122,7 @@ In addition to the above, this release updates [cesium-native](https://github.co
 - Added `CesiumMetadataValue`, which can hold a metadata value from `EXT_structural_metadata` while abstracting away its type.
 - Added a `distance` property to `CesiumOriginShift`, which specifies the maximum allowed distance from the current origin before it is shifted.
 - Added support for the `KHR_texture_transform` glTF extension - including rotation - in `baseColorTexture`, `metallicRoughnessTexture`, `emissiveTexture`, `normalTexture`, and `occlusionTexture`. The transformation is now applied on the GPU via nodes in the Material, rather than on the CPU by directly modifying texture coordinates.
-- Added `materialKey` to `CesiumRasterOverlay`, which matches the overlay to its corresponding parameters in the tileset's material. This allows for explicit ordering of raster overlays and overlay-specific effects. 
+- Added `materialKey` to `CesiumRasterOverlay`, which matches the overlay to its corresponding parameters in the tileset's material. This allows for explicit ordering of raster overlays and overlay-specific effects.
 - `CesiumCameraController` can now accept custom input actions that override the default inputs.
 
 ##### Fixes :wrench:

Runtime/Cesium3DTileset.cs

@@ -21,7 +21,12 @@ public enum CesiumDataSource
         /// <summary>
         /// The dataset is from a regular web URL.
         /// </summary>
-        FromUrl
+        FromUrl,
+
+        /// <summary>
+        /// The dataset is generated from the georeference ellipsoid.
+        /// </summary>
+        FromEllipsoid
     }
 
     /// <summary>

native~/Runtime/src/Cesium3DTilesetImpl.cpp

@@ -7,6 +7,7 @@
 #include "UnityTileExcluderAdaptor.h"
 #include "UnityTilesetExternals.h"
 
+#include <Cesium3DTilesSelection/EllipsoidTilesetLoader.h>
 #include <Cesium3DTilesSelection/Tileset.h>
 #include <CesiumGeospatial/GlobeTransforms.h>
 #include <CesiumIonClient/Connection.h>
@@ -694,6 +695,12 @@ void Cesium3DTilesetImpl::LoadTileset(
       // Resolve the API URL if it's not already in progress.
       resolveCesiumIonApiUrl(tileset.ionServer());
     }
+  } else if (
+      tileset.tilesetSource() ==
+      CesiumForUnity::CesiumDataSource::FromEllipsoid) {
+    this->_pTileset = EllipsoidTilesetLoader::createTileset(
+        createTilesetExternals(tileset),
+        options);
   } else {
     this->_pTileset = std::make_unique<Tileset>(
         createTilesetExternals(tileset),