Mapbox-gl -> d3 projection

This example shows how to convert from a Mapbox-gl map projection to a d3.geo Mercator projection. This allows you to take full advantage of all the d3.geo based functions and examples while also leveraging the power and ease-of-use of mapbox-gl

Much credit goes to @vicapow who developed viewport-mercator-project where he figured out the necessary calculations to make this work.

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
  <script src="//d3js.org/topojson.v1.min.js"></script>
  <script src="viewport.js"></script>
  
  <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.12.0/mapbox-gl.js'></script>
  <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.12.0/mapbox-gl.css' rel='stylesheet' />

circle.mapbox {
      stroke: #111;
      fill-opacity: 0.1;
    }
    circle.vp {
      fill-opacity: 0.1;
      stroke: #111;
    }
    circle.d3 {
      fill-opacity: 0.1;
      stroke-width: 3;
      stroke: orange;
    }
  </style>
</head>

<body>
  <div id="map"></div>
  <svg id="overlay2"></svg>
  <script>
  
    mapboxgl.accessToken = 'pk.eyJ1IjoiZW5qYWxvdCIsImEiOiJjaWhtdmxhNTIwb25zdHBsejk0NGdhODJhIn0.2-F2hS_oTZenAWc0BMf_uw'
    
    //Setup mapbox-gl map
    var map = new mapboxgl.Map({
      container: 'map', // container id
      style: "mapbox://styles/mapbox/light-v9",
      center: [-0.1,51.5119112],
      zoom: 11.5,
      
    })
    //map.scrollZoom.disable()
    map.addControl(new mapboxgl.Navigation());

// Setup our svg layer that we can manipulate with d3
    var container = map.getCanvasContainer()
    var svg = d3.select(container).append("svg")

// we can project a lonlat coordinate pair using mapbox's built in projection function
    function mapboxProjection(lonlat) {
      var p = map.project(new mapboxgl.LngLat(lonlat[0], lonlat[1]))
      return [p.x, p.y];
    }

// we can use viewport-mercator-project to get projection and unprojection functions
    function getVP() {
      var bbox = document.body.getBoundingClientRect();
      var center = map.getCenter();
      var zoom = map.getZoom();
      var vp = ViewportMercator({
        longitude: center.lng,
        latitude: center.lat,
        zoom: zoom,
        width: bbox.width,
        height: bbox.height,
      })
      return vp;
    }
    
    
    // we calculate the scale given mapbox state (derived from viewport-mercator-project's code)
    // to define a d3 projection
    function getD3() {
      var bbox = document.body.getBoundingClientRect();
      var center = map.getCenter();
      var zoom = map.getZoom();
      // 512 is hardcoded tile size, might need to be 256 or changed to suit your map config
      var scale = (512) * 0.5 / PI * pow(2, zoom);

var d3projection = d3.geo.mercator()
        .center([center.lng, center.lat])
        .translate([bbox.width/2, bbox.height/2])
        .scale(scale);

return d3projection;
    }
    
    // calculate the original viewport-mercator-project projection
    var vp = getVP();
        
    // calculate the original d3 projection
    var d3Projection = getD3()
    
    // we want to render the same point
    var point = [-0.1,51.5119112]
  
    var mapboxCircle = svg.append("circle").classed("mapbox", true)
    var vpCircle = svg.append("circle").classed("vp", true)
    var d3Circle = svg.append("circle").classed("d3", true)

// you can use any of these projections to create a d3.geo.path
    // function for rendering lines and polygons
    /*
    var path = d3.geo.path()
      .projection(mapboxProjection)
    */
    /*
    var path = d3.geo.path()
      .projection(d3Projection)
    */

function render() {
      
      // we update our calculated projections whenever the underlying map changes 
      // due to zoom and pan
      vp = getVP();
      d3Projection = getD3();

mapboxCircle.attr({
        cx: mapboxProjection(point)[0],
        cy: mapboxProjection(point)[1],
        r: 15// * currentScale
      })

vpCircle.attr({
        cx: vp.project(point)[0],
        cy: vp.project(point)[1],
        r: 20// * currentScale
      })

d3Circle.attr({
        cx: d3Projection(point)[0],
        cy: d3Projection(point)[1],
        r: 25// * currentScale
      })
    }

// re-render our visualization whenever the view changes
    map.on("viewreset", function() {
      render()
    })
    map.on("move", function() {
      render()
    })

// render our initial visualization
    render()

</script>
</body>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js

https://d3js.org/topojson.v1.min.js

https://api.tiles.mapbox.com/mapbox-gl-js/v0.12.0/mapbox-gl.js