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Additions to Point Cloud spec #733

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Feb 7, 2023
Merged

Additions to Point Cloud spec #733

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39ad1f7
Add note about sRGB colors in pnts spec
j9liu Feb 3, 2023
7b364ca
Note sRGB -> linear RGB in migration guide
j9liu Feb 3, 2023
41a36ea
Require POINTS_LENGTH to be greater than zero
j9liu Feb 3, 2023
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4 changes: 3 additions & 1 deletion specification/TileFormats/PointCloud/README.adoc
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Expand Up @@ -175,7 +175,7 @@ These semantics define global properties for all points.

| `POINTS_LENGTH`
| `uint32`
| The number of points to render. The length of each array value for a point semantic should be equal to this.
| The number of points to render. This must be greater than zero. The length of each array value for a point semantic should be equal to this.
| Yes.

| `RTC_CENTER`
Expand Down Expand Up @@ -246,6 +246,8 @@ Compressed attributes should be decompressed before any other transforms are app

If more than one color semantic is defined, the precedence order is `RGBA`, `RGB`, `RGB565`, then `CONSTANT_RGBA`. For example, if a tile's Feature Table contains both `RGBA` and `CONSTANT_RGBA` properties, the runtime would render with per-point colors using `RGBA`.

Point colors are defined in sRGB color space.

If no color semantics are defined, the runtime is free to color points using an application-specific default color.

In any case, xref:{url-specification-styling}README.adoc#styling-styling[3D Tiles Styling] may be used to change the final rendered color and other visual properties at runtime.
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1 change: 1 addition & 0 deletions specification/TileFormats/glTF/MIGRATION.adoc
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Expand Up @@ -57,6 +57,7 @@ xref:{url-specification-tileformats-pointcloud}README.adoc#tileformats-pointclou
* https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_meshopt_compression[`EXT_meshopt_compression`] and https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization[`KHR_mesh_quantization`] may be used for point cloud compression. link:https://github.com/CesiumGS/3d-tiles/tree/main/extensions/3DTILES_draco_point_compression/[`3DTILES_draco_point_compression`] is not directly supported in glTF because https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_draco_mesh_compression[`KHR_draco_mesh_compression`] only supports triangle meshes.
* Batch IDs and Batch Tables can be represented using https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_mesh_features[`EXT_mesh_features`] and https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_structural_metadata[`EXT_structural_metadata`].
* `CONSTANT_RGBA` is not directly supported in glTF, but can be achieved with materials or per-point colors.
* If `COLOR` or `CONSTANT_RGBA` are present, they should be converted from sRGB to linear RGB in the glTF.

.Point Clouds in 3D Tiles 1.0, and the corresponding representation in 3D Tiles 1.1
image::figures/migration-pnts.png[pnts]
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