D3 Examples - Raster & Vector III

Raster & Vector III

Using d3-tile to display raster image tiles underneath some TopoJSON vectors, and d3-zoom for pan & zoom. This version adjusts the transform and stroke-width to update the displayed vector data efficiently. You can instead reproject interactively, but changing the transform is typically much faster. Also see the static version.

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
body {
  margin: 0;
}
​
path {
  fill: none;
  stroke: red;
  stroke-linejoin: round;
  stroke-width: 1.5px;
}
​
</style>
<svg></svg>
<script src="//d3js.org/d3.v4.min.js"></script>
<script src="//d3js.org/d3-tile.v0.0.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>
​
var pi = Math.PI,
    tau = 2 * pi;
​
var width = Math.max(960, window.innerWidth),
    height = Math.max(500, window.innerHeight);
​
// Initialize the projection to fit the world in a 1×1 square centered at the origin.
var projection = d3.geoMercator()
    .scale(1 / tau)
    .translate([0, 0]);
​
var path = d3.geoPath()
    .projection(projection);
​
var tile = d3.tile()
    .size([width, height]);
​
var zoom = d3.zoom()
    .scaleExtent([1 << 11, 1 << 14])
    .on("zoom", zoomed);
​
var svg = d3.select("svg")
    .attr("width", width)
    .attr("height", height);
​
var raster = svg.append("g");
​
var vector = svg.append("path");
​
d3.json("/../../data/us.json", function(error, us) {
  if (error) throw error;
​
  // Compute the projected initial center.
  var center = projection([-98.5, 39.5]);
​
  // Apply a zoom transform equivalent to projection.{scale,translate,center}.
  svg
      .call(zoom)
      .call(zoom.transform, d3.zoomIdentity
          .translate(width / 2, height / 2)
          .scale(1 << 12)
          .translate(-center[0], -center[1]));
​
  vector
      .attr("d", path(topojson.mesh(us, us.objects.counties)));
});
​
function zoomed() {
  var transform = d3.event.transform;
​
  var tiles = tile
      .scale(transform.k)
      .translate([transform.x, transform.y])
      ();
​
  vector
      .attr("transform", transform)
      .style("stroke-width", 1 / transform.k);
​
  var image = raster
      .attr("transform", stringify(tiles.scale, tiles.translate))
    .selectAll("image")
    .data(tiles, function(d) { return d; });
​
  image.exit().remove();
​
  image.enter().append("image")
      .attr("xlink:href", function(d) { return "https://" + "abc"[d[1] % 3] + ".tile.openstreetmap.org/" + d[2] + "/" + d[0] + "/" + d[1] + ".png"; })
      .attr("x", function(d) { return d[0] * 256; })
      .attr("y", function(d) { return d[1] * 256; })
      .attr("width", 256)
      .attr("height", 256);
}
​
function stringify(scale, translate) {
  var k = scale / 256, r = scale % 1 ? Number : Math.round;
  return "translate(" + r(translate[0] * scale) + "," + r(translate[1] * scale) + ") scale(" + k + ")";
}
​
</script>
​
    