Take RealityTile.transformToRoot into account in loadGeometryFromStream

common/api/core-frontend.api.md

@@ -8430,7 +8430,7 @@ export class RealityTile extends Tile {
     selectSecondaryTiles(_args: TileDrawArgs, _context: TraversalSelectionContext): void;
     // @internal (undocumented)
     setContent(content: RealityTileContent): void;
-    // @internal (undocumented)
+    // @internal
     readonly transformToRoot?: Transform;
     // @internal (undocumented)
     readonly tree: RealityTileTree;

common/changes/@itwin/core-frontend/eringram-reprojectgeometry-bugfix_2025-12-01-20-32.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/core-frontend",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/core-frontend"
+}

core/frontend/src/internal/tile/RealityModelTileTree.ts

@@ -534,6 +534,7 @@ class RealityModelTileLoader extends RealityTileLoader {
     const thisParentId = parentId.length ? (`${parentId}_${childId}`) : childId;
     if (foundChild.transform) {
       const thisTransform = RealityModelTileUtils.transformFromJson(foundChild.transform);
+      // Accumulate tile's transform to apply it to this tile's children
       transformToRoot = transformToRoot ? transformToRoot.multiplyTransformTransform(thisTransform) : thisTransform;
     }
 

core/frontend/src/internal/tile/RealityTileLoader.ts

@@ -88,7 +88,13 @@ export abstract class RealityTileLoader {
     if (reader)
       reader.defaultWrapMode = GltfWrapMode.ClampToEdge;
 
-    const geom = reader?.readGltfAndCreateGeometry(tile.tree.iModelTransform);
+    let transform = tile.tree.iModelTransform;
+    if (tile.transformToRoot) {
+      transform = transform.multiplyTransformTransform(tile.transformToRoot);
+    }
+
+    const geom = reader?.readGltfAndCreateGeometry(transform);
+    // See RealityTileTree.reprojectAndResolveChildren for how reprojectionTransform is calculated
     const xForm = tile.reprojectionTransform;
     if (tile.tree.reprojectGeometry && geom?.polyfaces && xForm) {
       const polyfaces = geom.polyfaces.map((pf) => pf.cloneTransformed(xForm));

core/frontend/src/tile/RealityTile.ts

@@ -56,7 +56,9 @@ const scratchFrustum = new Frustum();
  * @public
  */
 export class RealityTile extends Tile {
-  /** @internal */
+  /** Transform to go from tile's local coordinate system to the root tile's corodinate system.
+   * @see [[RealityModelTileLoader.findTileInJson]] to see how the transformToRoot is calculated.
+   * @internal */
   public readonly transformToRoot?: Transform;
   /** @internal */
   public readonly additiveRefinement?: boolean;

core/frontend/src/tile/RealityTileTree.ts

@@ -415,6 +415,7 @@ export class RealityTileTree extends TileTree {
 
           const reprojectedCoords = response.iModelCoords;
           const dbToRoot = expectDefined(rootToDb.inverse());
+          // Interpolate between the original and reprojected points
           const getReprojectedPoint = (original: Point3d, reprojectedXYZ: XYZProps) => {
             scratchPoint.setFromJSON(reprojectedXYZ);
             const cartesianDistance = this.cartesianRange.distanceToPoint(scratchPoint);