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Gsplat fixedframe transform #12926

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Gsplat fixedframe transform #12926

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9c9c5eb
Switches to a fixed frame transform which fixes cases where the tiles…
keyboardspecialist Sep 25, 2025
520ebd9
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keyboardspecialist Sep 25, 2025
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1 change: 1 addition & 0 deletions CHANGES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
- Improved performance and reduced memory usage of `Event` class. [#12896](https://github.com/CesiumGS/cesium/pull/12896)
- Fixes vertical misalignment of glyphs in labels with small fonts [#8474](https://github.com/CesiumGS/cesium/issues/8474)
- Prevent runtime errors for certain forms of invalid PNTS files [#12872](https://github.com/CesiumGS/cesium/issues/12872)
- Fixes precision issues with Gaussian splat tilesets where tiles have a world transform and the tileset does not [#12925](https://github.com/CesiumGS/cesium/issues/12925)

#### Additions :tada:

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12 changes: 10 additions & 2 deletions packages/engine/Source/Scene/GaussianSplatPrimitive.js
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ import Quaternion from "../Core/Quaternion.js";
import SplitDirection from "./SplitDirection.js";
import destroyObject from "../Core/destroyObject.js";
import ContextLimits from "../Renderer/ContextLimits.js";
import Transforms from "../Core/Transforms.js";

const scratchMatrix4A = new Matrix4();
const scratchMatrix4B = new Matrix4();
Expand Down Expand Up @@ -427,6 +428,13 @@ GaussianSplatPrimitive.transformTile = function (tile) {
const gltfPrimitive = tile.content.gltfPrimitive;
const gaussianSplatPrimitive = tile.tileset.gaussianSplatPrimitive;

if (gaussianSplatPrimitive._rootTransform === undefined) {
gaussianSplatPrimitive._rootTransform = Transforms.eastNorthUpToFixedFrame(
tile.tileset.boundingSphere.center,
);
}
const rootTransform = gaussianSplatPrimitive._rootTransform;

const computedModelMatrix = Matrix4.multiplyTransformation(
computedTransform,
gaussianSplatPrimitive._axisCorrectionMatrix,
Expand All @@ -441,7 +449,7 @@ GaussianSplatPrimitive.transformTile = function (tile) {

const toGlobal = Matrix4.multiply(
tile.tileset.modelMatrix,
Matrix4.fromArray(tile.tileset.root.transform),
Matrix4.fromArray(rootTransform),
scratchMatrix4B,
);
const toLocal = Matrix4.inverse(toGlobal, scratchMatrix4C);
Expand Down Expand Up @@ -765,7 +773,7 @@ GaussianSplatPrimitive.buildGSplatDrawCommand = function (

const modelMatrix = Matrix4.multiply(
tileset.modelMatrix,
Matrix4.fromArray(tileset.root.transform),
Matrix4.fromArray(primitive._rootTransform),
scratchMatrix4B,
);

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