REVISION_HISTORY.md

June 5, 2023 · View on GitHub

This is the revision history for the extensions that have been developed as part of the "3D Tiles Next" effort, leading to the final release of 3D Tiles 1.1, and including the proposed glTF extensions.

November 2020

Added 3D Metadata Specification (draft version 0.0.0)
Added 3DTILES_metadata extension (draft version 0.0.0)
Added 3DTILES_content_gltf extension (draft version 0.0.0)
Added EXT_feature_metadata glTF extension (draft version 0.0.0)

February 2021

Added 3D Metadata Semantic Reference (draft version 1.0.0)
Added 3DTILES_implicit_tiling extension (draft version 0.0.0)
Added 3DTILES_multiple_contents extension (draft version 0.0.0)
Updated 3D Metadata Specification
- Updated to draft version 1.0.0
- The specification has been revised to focus on the core concepts of schemas (including classes, enums, and properties) and formats for encoding metadata. It is now language independent. The JSON schema has been removed.
- Added schemas which contain classes and enums
Updated schema definition
- Removed FLOAT16 type
- Removed BLOB type and blobByteLength property
- Removed stringByteLength property
- Added semantic property
- Added ENUM to the list of supported types and component types and added enumType to refer to the chosen enum
- min and max are now numbers instead of single-element arrays for non-ARRAY properties
Updated property table definition
- Removed offsetBufferViews, replaced with arrayOffsetBufferView and stringOffsetBufferView
- Removed name and description
- Removed elementCount and redefined count to mean the element count
Updated 3DTILES_metadata extension
- Updated to draft version 1.0.0
- Updated schema definition. See notes above.
Updated EXT_feature_metadata extension
- Updated to draft version 1.0.0
- Updated schema definition. See notes above.
- Updated property table definition. See notes above.
- Removed classes dictionary. Classes and enums are now contained in the schema object.
- Added schema and schemaUri. The schema object contains class and enum definitions. schemaUri refers to an external schema JSON file. schema and schemaUri are mutually exclusive.
- Added optional statistics object which provides aggregate information about select properties within the model
- Added EXT_feature_metadata extension to the EXT_mesh_gpu_instancing extension for assigning metadata to instances
- Removed vertexStride and instanceStride
- Added divisor for incrementing feature IDs at fixed intervals, e.g. per-triangle or per-quad

October 2021

Added 3DTILES_bounding_volume_s2 extension (draft version 0.0.0)
Updated 3D Metadata Specification
- Updated to draft version 2.0.0
- Removed raster encoding. Storing metadata in texture channels remains a valid implementation of this specification, but is not within the scope of this document.
- Removed table layout from the JSON encoding; each entity is encoded as a single JSON object.
Updated 3D Metadata Semantic Reference
- Updated to draft version 2.0.0
- Reorganize document to distinguish general and 3D Tiles-specific semantics
- Added clarification for units of distance and angles
- Added DESCRIPTION semantic
- Changed TILE_HORIZON_OCCLUSION_POINT and CONTENT_HORIZON_OCCLUSION_POINT type from ARRAY to VEC3
Updated schema definition
- Removed optional and added required. Properties are now assumed to be optional unless required is true.
- Added noData for specifying a sentinel value that indicates missing data
- Removed default
- NaN and Infinity are now explicitly disallowed as property values
- Added vector and matrix types: VEC2, VEC3, VEC4, MAT2, MAT3, MAT4
- Refactored type and componentType to avoid overlap. Properties that store a single value now have a type of SINGLE and a componentType of the desired type (e.g. type: "SINGLE", componentType: "UINT8")
- Class IDs, enum IDs, and property IDs must now contain only alphanumeric and underscore characters
- Add name and description to schema, class, and enum definitions
- Add id to schema definitions
Updated property table definition
- Split offsetType into arrayOffsetType and stringOffsetType
- Relaxed buffer view alignment to component size, rather than strict 8-byte boundaries
Updated 3DTILES_metadata extension
- Updated to draft version 2.0.0
- Updated schema definition. See notes above.
- Group IDs must now contain only alphanumeric and underscore characters
- Removed incomplete styling section
- Recommend _* prefix for application-specific summary statistics
- Removed name and description from entity schemas. Entities should use properties with equivalent semantics instead.
- The groups that are defined in a tileset are now given as an array. Each group has a unique identifier.
Updated 3DTILES_implicit_tiling extension
- Updated to draft version 1.0.0
- Updated property table definition. See notes above.
Renamed EXT_feature_metadata to EXT_mesh_features, including the following updates:
- Updated to draft version 2.0.0
- Updated schema definition. See notes above.
- Updated property table definition. See notes above.
- Renamed constant to offset, and divisor to repeat
- Removed statistics property, to be considered as a future extension
- Renamed featureTable to propertyTable and featureTexture to propertyTexture
- Removed featureIdAttributes and featureIdTextures, replaced with featureIds
- Primitives and nodes may now have feature IDs without associated property tables
- Removed string ID references to property tables and textures, replaced with integer IDs
- Feature ID values outside the range [0, count - 1] now indicate "no associated feature"
- Byte offsets for buffer views in a GLB-stored BIN chunk are no longer different from the core glTF specification
- Renamed _FEATURE_ID_# to FEATURE_ID_#
- Clarified that nodes with GPU instancing cannot reference property textures
- For GPU instance metadata, the EXT_mesh_features extension is now scoped to the node extensions instead of nesting inside the EXT_mesh_gpu_instancing extension.
- Refactored the property texture schema so it is now a glTF textureInfo object. All property values must be packed into a single texture.
- Property textures are now assumed to be in linear space, and must use nearest or linear filtering

February 2022

Updated 3D Metadata Specification
- Updated to draft version 3.0.0
- Updated schema definition. See notes below.
Updated 3D Metadata Semantic Reference
- Updated to draft version 3.0.0
- CONTENT_* semantics should now be assigned to content metadata properties instead of tile metadata properties
- Added ATTRIBUTION_IDS and ATTRIBUTION_STRINGS semantics for providing data attribution at multiple levels of granularity
- Added TILESET_FEATURE_ID_LABELS semantic to list the feature ID labels present in glTF content referenced by the tileset
- Added TILESET_CRS_GEOCENTRIC semantic to describe the geocentric coordinate reference system of the tileset
- Added TILESET_CRS_COORDINATE_EPOCH semantic to describe the coordinate epoch of vertex data
- Added TILE_BOUNDING_S2_CELL semantic
- Added TILE_REFINE semantic
- Added TILE_TRANSFORM semantic
- Added CONTENT_BOUNDING_S2_CELL semantics
- Added CONTENT_URI semantic
- Added CONTENT_GROUP_ID semantic
Updated schema definition
- type is required and must be one of the following: SCALAR, VEC2, VEC3, VEC4, MAT2, MAT3, MAT4, STRING, BOOLEAN, ENUM
- componentType is required for scalar, vector, and matrix types and must be one of the following: INT8, UINT8, INT16, UINT16, INT32, UINT32, INT64, UINT64, FLOAT32, FLOAT64
- Arrays are now distinct from the type system
  - Removed ARRAY type and componentCount property; replaced with array and count properties. array is a boolean that indicates whether the property is an array. When count is defined the property is a fixed-length array. Otherwise the property is a variable-length array.
  - Arrays of vectors and matrices are now supported
- Added offset and scale which are used to transform property values into a different range. Useful for quantized property values.
- Added back default
- Schema id property is now required
Updated property table definition
- Renamed bufferView to values
- Renamed stringOffsetBufferView to stringOffsets
- Renamed arrayOffsetBufferView to arrayOffsets
- Added offset and scale which are used to transform property values into a different range. When present, these override the class property's offset and scale.
- Added min and max which store the minimum and maximum property values.
Updated 3DTILES_metadata extension
- Updated to draft version 3.0.0
- Updated schema definition. See notes above.
- Added content metadata. A content may specify its class and property values with the 3DTILES_metadata content extension object.
- Removed the implicit tiling 3DTILES_metadata extension. Tile metadata is now provided by the tileMetadata subtree property.
Updated 3DTILES_implicit_tiling extension
- Updated to draft version 2.0.0
- Updated property table definition. See notes above.
- Changed maximumLevel to availableLevels for consistency with subtreeLevels. Note that maximumLevel is an index whereas availableLevels is a length: availableLevels is equivalent to maximumLevel + 1.
- Content availability for multiple contents is now provided by the contentAvailability property instead of a separate 3DTILES_multiple_contents extension. contentAvailability is now an array of availability objects.
- Added top-level propertyTables array to subtree format.
- Tile metadata is now provided by the tileMetadata property instead of a separate 3DTILES_metadata extension. tileMetadata refers to a property table containing metadata about available tiles.
- Content metadata is now provided by the contentMetadata property. Each array element refers to a property table containing metadata about available content.
- Subtree metadata is now provided by the subtreeMetadata object. Subtree metadata is encoded in JSON, similar to tileset metadata.
- Renamed availability bufferView to bitstream
- Added JSON subtree format as an alternative to the binary subtree format
Updated 3DTILES_multiple_contents extension
- Updated to draft version 1.0.0
- Renamed content to contents
- Removed the implicit tiling 3DTILES_multiple_contents extension. Content availability for multiple contents is now provided by the contentAvailability subtree property.
Split the EXT_mesh_features extension into three separate extensions:
- EXT_mesh_features that only defines the concept of feature IDs
- EXT_structural_metadata that allows associating the features with metadata
- EXT_instance_features that supports GPU instance feature IDs.
Updated EXT_mesh_features extension
- Updated to draft version 3.0.0
- Removed the "Implicit Feature IDs" concept. There have not been enough practical use-cases that could justify including them.
- Renamed FEATURE_ID_# back to _FEATURE_ID_#: The underscore is required for custom attributes, according to the glTF specification, and without it, the assets do not pass validation.
- The featureIds and the propertyTables had been stored as parallel arrays, and the connection between them had been established implicitly, by them appearing at the same index in their respective array. Now each feature ID set can explicitly contain propertyTable, which is the index of the property table that it refers to.
- Added optional label property to identify feature ID sets across different glTF primitives and assets.
- Instead of having dedicated classes for "Attribute Feature IDs" and "Texture Feature IDs", there is one common "Feature ID" class that either stores the attribute or the texture, respectively.
- Added featureId.nullFeatureId, which can be used as a value indicating that a certain element is not associated with a feature ID.
- Added featureId.featureCount, which is the number of distinct, non-null feature ID values.
- Changed the channel for feature ID textures to be a channels array, so that multiple channels can be combined into one feature ID, allowing for more than 256 feature ID values in feature ID textures.
Added EXT_structural_metadata extension (draft version 0.0.0)
- Updated property table definition. See notes above.
- Update schema definition. See notes above.
- Updated property texture definition
  - Properties are no longer required to be packed into the same texture. The number of class properties is no longer constrained by the number of texture channels.
  - Each item in the properties dictionary is now a textureInfo object
  - Added offset and scale which are used to transform property values into a different range. When present, these override the class property's offset and scale.
  - Added min and max which store the minimum and maximum property values in the texture.
- Added propertyAttributes, and additional metadata encoding for vertex data, in particular point clouds
Added EXT_instance_features extension (draft version 0.0.0)