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MIGRATION.adoc

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Migration From Legacy Tile Formats

This section describes how legacy tile formats can be converted into equivalent glTF content.

Batched 3D Model (b3dm)

Batched 3D Model is a wrapper around a binary glTF that includes additional information in its Feature Table and Batch Table. Batched 3D Model content can be converted into glTF content with the following changes:

b3dm
Figure 1. Batched 3D Models in 3D Tiles 1.0, and the corresponding representation in 3D Tiles 1.1

Instanced 3D Model (i3dm)

Instanced 3D Model instances a glTF asset (embedded or external) and provides per-instance transforms and batch IDs.

  • The RTC_CENTER can be added to the translation component of the root node of the glTF asset.

  • glTF can leverage GPU instancing with the EXT_mesh_gpu_instancing extension.

  • Batch IDs and Batch Tables can be represented using EXT_instance_features and EXT_structural_metadata.

  • EAST_NORTH_UP is not directly supported, but can be represented using per-instance rotations.

i3dm
Figure 2. Instanced 3D Models in 3D Tiles 1.0, and the corresponding representation in 3D Tiles 1.1

Point Cloud (pnts)

Point Cloud can be represented as a glTF using the primitive mode 0 (POINTS).

  • The RTC_CENTER can be added to the translation component of the root node of the glTF asset.

  • Feature table properties like POSITION, COLOR, and NORMAL may be stored as glTF attributes.

  • EXT_meshopt_compression and KHR_mesh_quantization may be used for point cloud compression. 3DTILES_draco_point_compression is not directly supported in glTF because KHR_draco_mesh_compression only supports triangle meshes.

  • Batch IDs and Batch Tables can be represented using EXT_mesh_features and 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.

pnts
Figure 3. Point Clouds in 3D Tiles 1.0, and the corresponding representation in 3D Tiles 1.1

Composite (cmpt)

All inner contents of a Composite may be combined into the same glTF as separate nodes, meshes, or primitives, at the tileset author’s discretion. Alternatively, a tile may have multiple contents.