open-vector-tile

About

A Modified TypeScript implementation of the Mapbox Vector Tile library. It is backwards compatible but offers a lot of new features and improvements including (but not limited to):

• 🔗 lightweight zero dependency builds.
• 🌴 Proper module treeshake.
• 🦺 Complete TypeScript support / safety.
• 🗜 Pre-Tessellated & Indexed geometries to quickly ship data to the renderer.
• 🧊 Support for 3D geometries.
• ♏ Support for M-Values for each geometry point (used by lines and polygons).
• ♻️ Feature Properties & M-Values are stored as "Shapes" which reuses objects only needing to do lookups on values.
• 🏛 Column encoding of data to make it more compact. Better gzip and brotli compression.
• 🪺 Support nested objects in properties and m-values.
• 📦 All features support first class citizen BBOX data like IDs.
• 🫥 Lines and Polygons support offsets to know the distance it's traveled (useful for correctly rendering dashed lines across tiles).

Inspiration

A very talented Markus Tremmel came up with the idea of migrating away from a row based approach to a column based approach with his COVTiles. I wanted to test the idea of simplifying his project and see if it was worth the effort. Once I saw brotli compression had comperable results, I decided to finish the project.

Motivations

Since another spec is being built at the same time, you may think this is a waste of time or creating an unnecessary conflict of interest. So I wrote my thoughts on this topic and why this spec is being created.

Read The Spec

open-vector-tile-spec

Install

#bun
bun add open-vector-tile
# pnpm
pnpm add open-vector-tile
# yarn
yarn add open-vector-tile
# npm
npm install open-vector-tile

# cargo
cargo install open-vector-tile
Copy

Project Structure

Example use

const fs = from 'fs'
import { VectorTile } from 'open-vector-tile'

// assume you can read (.pbf | .mvt | .ovt)
const fixture = fs.readFileSync('./x-y-z.vector.pbf')
// Bun const fixture = new Uint8Array(await Bun.file('./x-y-z.vector.pbf').arrayBuffer())
// load the protobuf parsing it directly
const tile = new VectorTile(fixture)

console.log(tile)

// example layer
const { landuse } = tile.layers

// grab the first feature
console.log(landuse.feature(0))
console.log(landuse.feature(0).loadGeometry())
Copy

General Purpose API

Tile

Read in a Tile

const tile = new VectorTile(uint8Array)
Copy

Read in a layer

const layer = tile.layers[layerName]
Copy

Layers

Layer Properties

type Extents = 512 | 1_024 | 2_048 | 4_096 | 8_192 | 16_384
interface Layer {
    // version control helps know what features are available
    version: number;
    // name of the layer
    name: string;
    // extent of the vector tile. MUST be one of `512`, `1024`, `2048`, `4096`, `8192`, or `16384`
    extent: Extents;
    // number of features in the layer
    length: number;
}
Copy

Read in a Feature

// returns a VectorFeature
const feature = layer.feature(index)
Copy

Features

Feature Types

// 6 feature types in total plus the old MapboxVectorFeature
export type VectorFeature =
  // points may be a collection of points or single point
  | OVectorPointsFeature
  // lines may be a collection of lines or single line
  | OVectorLinesFeature
  // polygons may be a collection of polygons or single polygon
  | OVectorPolysFeature
  // 3D points may be a collection of 3D points or single 3D point
  | OVectorPoints3DFeature
  // 3D lines may be a collection of 3D lines or single 3D line
  | OVectorLines3DFeature
  // 3D polygons may be a collection of 3D polygons or single 3D polygon
  | OVectorPolys3DFeature
  // Can be any form of points, lines, or polygons without any of the new features
  // but all the functions. line offsets and bbox will always be defaults.
  | MapboxVectorFeature;
Copy

Feature Properties

type Extents = 512 | 1_024 | 2_048 | 4_096 | 8_192 | 16_384
interface Feature {
    // properties of the feature
    properties: any;
    // id of the feature
    id: number;
    // extent of the vector tile. MUST be one of `512`, `1_024`, `2_048`, `4_096`, `8_192`, or `16_384`
    extent: Extents;
}
Copy

Get the Feature's Bounding Box

export type BBox = [left: number, bottom: number, right: number, top: number];
export type BBox3D = [left: number, bottom: number, right: number, top: number, near: number, far: number];

const bbox: BBox | BBox3D = feature.bbox()
Copy

Pull in the geometry as a collection of points

// supported by all types, points, lines, and polygons
const geometry: Point[] | Point3D[] = feature.loadPoints()
Copy

Pull in the geometry as a collection of lines

// Supported by any line or polygon type
/// points will return an empty array
interface VectorLineWithOffset {
  /** the offset of the line to start processing the dash position */
  offset: number;
  /** the line data */
  geometry: VectorLine;
}
interface VectorLine3DWithOffset {
  /** the offset of the line to start processing the dash position */
  offset: number;
  /** the line data */
  geometry: VectorLine3D;
}
const geometry: VectorLineWithOffset[] | VectorLine3DWithOffset[] = feature.loadLines()
Copy

Pull in the geometry relative to the type

const pointFeature: Point[] = (feature as OVectorPointsFeature).loadGeometry()
const lineFeature: VectorLine[] = (feature as OVectorLinesFeature).loadGeometry()
const polyFeature: VectorPoly[] = (feature as OVectorPolysFeature).loadGeometry()
const point3DFeature: Point3D[] = (feature as OVectorPoints3DFeature).loadGeometry()
const line3DFeature: VectorLine3D[] = (feature as OVectorLines3DFeature).loadGeometry()
const poly3DFeature: VectorPoly3D[] = (feature as OVectorPolys3DFeature).loadGeometry()
Copy

If a Polygon type, Pull in the raw geometry with indices and tesselation data

// works for any polygon or polygon3D type.
// NOTE: If the indices is empty, then the geometry was never pre-earcut and you need to fallback to `loadGeometry` instead.
const geometry: [geometry: number[], indices: number[]] = feature.loadGeometryFlat()
Copy

Creating and Validating your Shapes

Shapes define the type of data that can be stored in the vector tile. They are explained in the specification.

If you'd like to validate the shape, feel free to use the Ajv library.

import Ajv from 'ajv';
import { ShapeSchema } from 'open-vector-tile'; // Path to the schema

import type { Shape } from 'open-vector-tile';

const ajv = new Ajv();
const validate = ajv.compile(ShapeSchema);

const shape: Shape = {
  a: 'i64',
  b: ['string'],
  c: {
    d: 'f64',
    e: 'bool',
    f: 'null',
    g: 'f32',
    h: {
      i: 'u64',
    },
  },
};

validate(shape); // true
Copy

---

Development

Requirements

You need the tool tarpaulin to generate the coverage report. Install it using the following command:

cargo install cargo-tarpaulin
Copy

The bacon coverage tool is used to generate the coverage report. To utilize the pycobertura package for a prettier coverage report, install it using the following command:

pip install pycobertura
Copy

Running Tests

To run the tests, use the following command:

# TYPESCRIPT
## basic test
bun run test
## live testing
bun run test:dev

# RUST
## basic test
cargo test
# live testing
bacon test
Copy

Generating Coverage Report

To generate the coverage report, use the following command:

cargo tarpaulin
# faster
cargo tarpaulin --color always --skip-clean
# bacon
bacon coverage # or type `l` inside the tool
Copy