Cesium3DTileset modelMatrix reset error

[wonphll536]

What happened?

I applied the transformation matrix to Cesium3DTileset and reapplied the initial value, but an error occurred.

Reproduction steps

1. Create Cesium3DTeilset
2. Clone the original modelMatrix
3. Apply any transformation matrix
4. Apply original modelMatrix ---> Error occurs after

I applied the above process to Sandcastle. If you wait a while after running, an error will occur.

Sandcastle example

https://sandcastle.cesium.com/#c=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

Environment

Browser: Chrome
CesiumJS Version: 1.117
Operating System: window10

[javagl]

(Edit: This was also posted in the forum at https://community.cesium.com/t/cesium3d-tileset-model-matrix-reset-error/32477 )

---

• When the transform is modified, then this will cause a call to Cesium3DTile.updateTransform, which updates the bounding volume of the tile by calling createBoundingVolume
• When the tile defines a region in its bounding volume header, it will create the tile bounding volume by calling createRegion
  • Important: It will pass in the current bounding volume of the tile as the result parameter, to be filled with the data from this region
• The createRegion function tries to fill the result parameter, assuming that it is a TileBoundingRegion
• But... when the transform changed, then the createRegion will not return a TileBoundingRegion. Instead, it will return a TileOrientedBoundingBox, by calling createBoxFromTransformedRegion

So to summarize: Changing the transform (by setting the modelMatrix) will convert all TileBoundingRegion into TileOrientedBoundingBox instances. Changing the transform again will trigger the update process, which find the region in the tile, and then assumes that the tile bounding volume is a TileBoundingRegion, even though it was previously changed to be a TileOrientedBoundingBox.

There could be some ... "pragmatic" ... fixes for this, involving some if (result instanceof TileOrientedBoundingBox) doNotTryToFillItWithRegionData(), but the details are to be sorted out...

[jjhembd]

This could be a one-line fix in the createRegion function in Cesium3DTile. We already check if the transform has been changed, and if so, return a TileOrientedBoundingBox instead of a TileBoundingRegion.

So this:

  if (
    !Matrix4.equalsEpsilon(transform, initialTransform, CesiumMath.EPSILON8)
  ) {
    return createBoxFromTransformedRegion(

could become this:

  if (
    !Matrix4.equalsEpsilon(transform, initialTransform, CesiumMath.EPSILON8) ||
    result instanceof TileOrientedBoundingBox
  ) {
    return createBoxFromTransformedRegion(