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README.md

⚠️ 3DTILES_draco_point_compression was deprecated in 3D Tiles 1.1. See pnts migration guide. ⚠️

3DTILES_draco_point_compression Extension

Contributors

Status

Complete

Dependencies

Written against the 3D Tiles 1.0 specification.

Optional vs. Required

This extension is required, meaning it must be placed in both the extensionsUsed and extensionsRequired lists in the tileset JSON.

Contents

Overview

This extension adds Draco geometry compression to the Point Cloud tile format to support streaming compressed point data.

Draco compresses common properties such as position, color, and normal, as well as generic metadata such as intensity or classification.

This extension is based on Draco bitstream version 2.2, which is normative and included in scope.

Point Cloud tile format updates

Feature Table

The Feature Table of a Point Cloud tile may be extended to include a 3DTILES_draco_point_compression object. This object defines the compressed properties and the location of the compressed data in the Feature Table binary.

Below is an example of a Feature Table with the Draco extension set:

{
    "POINTS_LENGTH": 20,
    "POSITION": {
        "byteOffset": 0
    },
    "RGB": {
        "byteOffset": 0
    },
    "BATCH_ID": {
        "byteOffset": 0,
        "componentType": "UNSIGNED_BYTE"
    },
    "extensions": {
        "3DTILES_draco_point_compression": {
            "properties": {
                "POSITION": 0,
                "RGB": 1,
                "BATCH_ID": 2
            },
            "byteOffset": 0,
            "byteLength": 100
        }
    }
}

properties

properties defines the Feature Table properties stored in the compressed data. In the example above, positions, RGB colors, and batch IDs are compressed.

Each property defined in the extension must correspond to a semantic already defined in the Feature Table JSON. When a semantic is compressed its byteOffset property is ignored and may be set to zero. Its componentType, if present, defines the component type of the uncompressed data.

Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID.

Allowed properties are "POSITION", "RGBA", "RGB", "NORMAL", and "BATCH_ID".

byteOffset

The byteOffset property specifies a zero-based offset relative to the start of the Feature Table binary at which the compressed data starts.

byteLength

The byteLength property specifies the length, in bytes, of the compressed data.

Schema updates

See Property reference for the 3DTILES_draco_point_compression Feature Table schema reference. The full JSON schema can be found in 3DTILES_draco_point_compression.featureTable.schema.json.

Batch Table

Per-point metadata can also be compressed. The Batch Table may be extended to include a 3DTILES_draco_point_compression object that defines additional compressed properties.

Below is an example of a Batch Table with the Draco extension set:

{
    "Intensity": {
        "byteOffset": 0,
        "type": "SCALAR",
        "componentType": "UNSIGNED_BYTE"
    },
    "Classification": {
        "byteOffset": 0,
        "type": "SCALAR",
        "componentType": "UNSIGNED_BYTE"
    },
    "extensions": {
        "3DTILES_draco_point_compression": {
            "properties": {
                "Intensity": 3,
                "Classification": 4
            }
        }
    }
}

properties

properties defines additional Batch Table properties stored in the compressed data. In the example above, intensity and classification are compressed.

Each property defined in the extension must correspond to a property name already defined in the Batch Table JSON. When a property is compressed its byteOffset property is ignored and may be set to zero. Its componentType and type properties define the component type and type, respectively, of the uncompressed data.

Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID.

byteOffset and byteLength are not defined in the Batch Table extension; all compressed data is stored in the Feature Table binary.

Schema updates

See Property reference for the 3DTILES_draco_point_compression Batch Table schema reference. The full JSON schema can be found in 3DTILES_draco_point_compression.batchTable.schema.json.

Notes

If some properties are compressed and others are not, the Draco encoder must apply the POINT_CLOUD_SEQUENTIAL_ENCODING encoding method. This ensures that Draco preserves the original ordering of point data.

Implementation Note: Draco may reorder point data to achieve better compression and smaller file sizes. For best results, all properties in the Feature Table and Batch Table should be Draco compressed, in which case POINT_CLOUD_SEQUENTIAL_ENCODING should not be applied.

Resources

This section is non-normative.

Property reference

3DTILES_draco_point_compression Feature Table extension

Specifies the compressed Feature Table properties and the location of the compressed data in the Feature Table binary.

Properties

Type Description Required
properties object Defines the properties stored in the compressed data. Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID. ✅ Yes
byteOffset number A zero-based offset relative to the start of the Feature Table binary at which the compressed data starts. ✅ Yes
byteLength number The length, in bytes, of the compressed data. ✅ Yes

properties ✅

Defines the properties stored in the compressed data. Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID.

  • Type: object
  • Required: Yes
  • Type of each property: number

byteOffset ✅

A zero-based offset relative to the start of the Feature Table binary at which the compressed data starts.

  • Type: number
  • Required: Yes
  • Minimum: >= 0

byteLength ✅

The length, in bytes, of the compressed data.

  • Type: number
  • Required: Yes
  • Minimum: >= 0

3DTILES_draco_point_compression Batch Table extension

Specifies the compressed Batch Table properties.

Properties

Type Description Required
properties object Defines the properties stored in the compressed data. Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID. ✅ Yes

properties ✅

Defines the properties stored in the compressed data. Each property is associated with a unique ID. This ID is used to identify the property within the compressed data. No two properties in the Feature Table and Batch Table may use the same ID.

  • Type: object
  • Required: Yes
  • Type of each property: number