glifchits / node-mvt-encoder

A Node.js utility to encode a vector tile schema into a Mapbox vector tile

node-mvt-encoder

A Node.js utility to encode a vector tile spec into a Mapbox vector tile.

Installation

npm install mvt-encoder

node-gdal is a dependency of this project. It requires gdal to be installed in your environment:

apt-get update -y && apt-get install -y libproj-dev gdal-bin

Usage

var tileEncode = require('mvt-encoder');
var VectorTile = require('@mapbox/vector-tile').VectorTile

var tileSpec = [{
  name: 'blocks',
  features: [{
    geometry: "POLYGON ((0 0, 0 1, 1 1, 1 0, 0 0))",
    properties: {
      hello: "world"
    }
  }]
}];

var encoded = tileEncode(tileSpec);
var decoded = new VectorTile(encoded)

console.log(decoded.layers)
// { blocks: VectorTileLayer {...} }

Tile specification

The tileEncode function exported in this module takes one parameter: a "tile spec". This was inspired by Mapzen's mapbox-vector-tile package.

A "tile spec" is an array of "layer specs".

a "layer spec" is an object with the properties:

• name: the name of the layer (string)
• features: an array of objects with the properties:
  • geometry: a WKT representation of a feature geometry. Coordinates are relative to the tile, scaled in the range [0, 4096)
  • properties: an object with arbitrary key/values.

Notes

• Only tested for Polygon features
• Does not quantize geometry to the tile grid
• Outputs Mapbox vector tile conforming to (at best) version 1 of the spec

node-mvt-encoder's Issues

Create benchmark and track performance

This module should be fast

Provide more meaningful error messages

Trying to integrate this module into an app I get:

  Error: Unsupported geometry type
      at features.forEach (/app/node_modules/mvt-encoder/tileEncoder.js:139:32)
      at Array.forEach (<anonymous>)
      at encodeFeatures (/app/node_modules/mvt-encoder/tileEncoder.js:138:12)

(provided EWKT from PostGIS, not a WKT)

or

  TypeError: Cannot read property 'count' of undefined
      at encodeGeometry (/app/node_modules/mvt-encoder/tileEncoder.js:74:45)
      at features.forEach (/app/node_modules/mvt-encoder/tileEncoder.js:144:17)
      at Array.forEach (<anonymous>)

(probably because I provided a MULTIPOLYGON)

Test cases to check:

• Unsupported input geometry (require WKT)
• Unsupported geometry during encoding (only support POLYGON for now)
• Coordinates not scaled to tile extent (forgot to translate them)

Document the tile schema

Put some info in the README about the expected tile schema.

Continuous testing

Tests are there, run them and show a status badge.

Publish as NPM package

Do some clean up to ensure this can be cleanly imported as a module with a simple API

Compile the vector tile protobuf schema

Don't do it on the fly since this incurs some overhead