QuadTiles

Inspired and guided by the Automatic Projection Tiles tech demo from Jason Davies and the source code by the same name 'd3.quadTiles.js'. https://www.jasondavies.com/maps/tile/

This utility takes a d3 geo projection and using the projection's clipping rectangles returns an array of visible tiles. A maximum tile budget and max zoom level controls the quadtree descent. A full hierarchy of visible tiles at zoom levels starting from 0 until the zoom level reached is also returned.

Use this algorithm to efficiently calculate visible map tiles on any d3 geo map projection! Performs well even at high zoom levels.

var d3 = require('d3');
var projection = d3.geo.orthographic()
  .precision(0.1)
  .clipAngle(90)
  .rotate([-150, 25])
  .scale(150)
  .translate([300, 240])
  .clipExtent([[0, 0], [600, 480]]);
var quadtiles = require('d3-quadtiles');
var quad = quadtiles(projection, { maxtiles: 32, maxzoom: 18 });
console.log(quad.zoom); // e.g. 6
console.log(quad.tiles); // e.g. [zoom6tile1, zoom6tile2, zoom6tile3..]
// quad.all is indexed by zoom level
console.log(quad.all); // e.g. [[zoom0tile1], [zoom1tile1, zoom1tile2], ...]
// tile = {
//   type: "Polygon",
//   key: [x, y, z], // tilespace coordinates
//   // points created as 10 points along each side of the tile starting top left and going right
//   // 40 points total
//   points: [[[lng, lat], [lng, lat], [lng, lat], ...]],
//   centroid: [lng, lat] // coordinates of centroid
// }