block by pnavarrc 5bb1a7c2b4c5b624bb83

Inverse Projection

Full Screen

index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">

  <title>Inverse Projection</title>

  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js"></script>
</head>
<body>

  <style>

  body {
    margin: 0;
  }

  svg {
    background-color: #4B4B55;
    cursor: crosshair;
  }

  .sphere {
    fill: none;
    stroke: #d6ff9f;
  }

  .coords {
    stroke: none;
    fill: #8DBD0C;
    font-family: 'Helvetica Neue', Helvetica, sans-serif;
  }

  .land {
    fill: #8DBD0C;
    fill-opacity: 0.25;
    stroke: #8DBD0C;
    stroke-width: 1;
  }
  </style>

  <div id="map-container"></div>

  <script>

    // Set the dimensions of the map
    var width  = 960,
        height = 480;

    // Create a selection for the container div and append the svg element
    var div = d3.select('#map-container'),
        svg = div.append('svg');

    // Set the size of the SVG element
    svg.attr('width', width).attr('height', height);

    // Create a text element to write the coordinates
    var label = svg.append('text')
      .classed('coords', true)
      .attr('x', 20)
      .attr('y', 30);

    // Create and configure a geographic projection
    var projection = d3.geo.equirectangular()
      .translate([width / 2, height / 2]);

    // Create and configure a path generator
    var pathGenerator = d3.geo.path()
      .projection(projection);

    // Create and configure the graticule generator (one line every 20 degrees)
    var graticule = d3.geo.graticule()
      .step([20, 20]);

    // Retrieve the geographic data asynchronously
    d3.json('land.topojson', function(err, data) {

      // Throw errors on getting or parsing the file
      if (err) { throw err; }

      // Convert the TopoJSON features to GeoJSON
      var features = topojson.feature(data, data.objects.land);

      // Sphere
      var sphere = svg.selectAll('path.sphere').data([{type: 'Sphere'}]);

      sphere.enter().append('path').classed('sphere', true);
      sphere.attr('d', pathGenerator);
      sphere.exit().remove();

      // Land
      var land = svg.selectAll('path.land').data([features]);

      land.enter().append('path').classed('land', true);
      land.attr('d', pathGenerator);
      land.exit().remove();

    });

    // Attach a listener for the mousemove event
    svg.on('mousemove', function(ev) {

      // Get the (x, y) position of the mouse (relative to the SVG element)
      var pos = d3.mouse(svg.node()),
          px = pos[0],
          py = pos[1];

      // Compute the corresponding geographic coordinates using the inverse projection
      var coords = projection.invert([px, py]);

      // Format the coordinates to have at most 4 decimal places
      var lon = coords[0].toFixed(4),
          lat = coords[1].toFixed(4);

      // Set the content of the label
      label.text([lat, lon].join(', '));
    });

  </script>

</body>
</html>

Makefile

# Download and Transform the 1:50m Country Shapefiles from Natural Earth
# http://www.naturalearthdata.com/downloads/110m-physical-vectors/

URL = http://www.naturalearthdata.com/http//www.naturalearthdata.com/download/110m/physical/ne_110m_land.zip

# Download the zip file from the Natural Earth server
ne_110m_land.zip:
	curl -LO $(URL)

# Unzip the shapefiles
ne_110m_land.shp: ne_110m_land.zip
	unzip ne_110m_land.zip
	touch ne_110m_land.shp

# Convert the shapefiles to GeoJSON
land.geojson: ne_110m_land.shp
	ogr2ogr -f GeoJSON land.geojson ne_110m_land.shp

# Convert the GeoJSON file to TopoJSON
land.topojson: land.geojson
	topojson -p -o land.topojson land.geojson

# Remove source and temporary files
clean:
	rm ne_110m_land*