Triangulate Topojson ( => Geojson) using earcut.js

triangulate-topojson.js

import earcut from 'earcut';
import topojson from 'topojson';
import math from 'mathjs';

const triangulateTopojson = (res) => {
  const totalStart = performance.now();

  const key = Object.keys(res.objects)[0];
  let start = performance.now();
  const geojson = topojson.mesh(res, res.objects[key]);
  let diff = performance.now() - start;
  console.log(`Topo - Converting topojson to geojson took ${math.round(diff, 2)} milliseconds`);
  // console.log(geojson);

  for (let i = 0; i < geojson.coordinates.length; i++) {
    const coordinates = geojson.coordinates[i];
    start = performance.now();
    const data = earcut.flatten([coordinates]);
    diff = performance.now() - start;
    console.log(`Topo - Flattening coordinates took ${math.round(diff, 2)} milliseconds`);
    // console.log(data);

    start = performance.now();
    const triangles = earcut(data.vertices, data.holes, data.dimensions);
    diff = performance.now() - start;
    console.log(`Topo - Triangulation generated ${triangles.length / 3} triangles, took ${math.round(diff, 2)} milliseconds`);

    // console.log(triangles);
    // const vertex = this.props.mapEngine.layer.fromLatLngToVertex(location);

    const vertices = data.vertices;

    start = performance.now();
    const verts = [];
    for (let j = 0; j < triangles.length; j += 3) {
      const a = triangles[j];
      const b = triangles[j + 1];
      const c = triangles[j + 2];
      verts.push([
        [vertices[a * 2], vertices[a * 2 + 1]],
        [vertices[b * 2], vertices[b * 2 + 1]],
        [vertices[c * 2], vertices[c * 2 + 1]]
      ]);
    }
    diff = performance.now() - start;
    console.log(`Topo - materilization of vertices took ${math.round(diff, 2)} milliseconds`);
    // console.log(verts);
  }

  diff = performance.now() - totalStart;
  console.log(`Topo - processing took ${math.round(diff, 2)} milliseconds`);
};