extensions
3DTILES_draco_point_compression

3DTILESdracopoint_compression Extension

# 3DTILES_draco_point_compression Extension

# Overview

This extension adds Draco geometry compression (opens new window) 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 (opens new window), 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.

Draco Open Source Library (opens new window)

# Property reference

3DTILES_draco_point_compression Feature Table extension
3DTILES_draco_point_compression Batch Table extension

# 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 ✅

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