Smooth GeoTIFF drawing with D3js - color scale

This example shows how to represent a GeoTIFF raster directly into a Canvas object.

The example is identical to this one, but with another way to create the color scales. This method makes easy to create all the complex color scales needed, and it's taken from the plotty library.

The color scale used here is taken from the colorbrewer2 site, with the name RdBu.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

</style>
<body>

var projection = d3.geoAzimuthalEqualArea()
    .rotate([-55.5, -24])
    .scale(1100);

var intervalsTemp = [14,17,20,23,26,29,35,38];

var canvas = d3.select("body").append("canvas")
    .attr("width", width)
    .attr("height", height);

var context = canvas.node().getContext("2d");
d3.request("tz850.tiff")
  .responseType('arraybuffer')
  .get(function(error, tiffData){
d3.json("world-110m.json", function(error, topojsonData) {
  var countries = topojson.feature(topojsonData, topojsonData.objects.countries);
  var path = d3.geoPath()
      .projection(projection).context(context);

context.beginPath();
  context.strokeStyle = "#777";
  context.fillStyle = "#aaa";
  path(countries);
  context.fill();
  context.stroke();

var tiff = GeoTIFF.parse(tiffData.response);
  var image = tiff.getImage();
  var rasters = image.readRasters();
  var tiepoint = image.getTiePoints()[0];
  var pixelScale = image.getFileDirectory().ModelPixelScale;
  var geoTransform = [tiepoint.x, pixelScale[0], 0, tiepoint.y, 0, -1*pixelScale[1]];
  var invGeoTransform = [-geoTransform[0]/geoTransform[1], 1/geoTransform[1],0,-geoTransform[3]/geoTransform[5],0,1/geoTransform[5]];

var tempData = new Array(image.getHeight());
  for (var j = 0; j<image.getHeight(); j++){
      tempData[j] = new Array(image.getWidth());
      for (var i = 0; i<image.getWidth(); i++){
          tempData[j][i] = rasters[1][i + j*image.getWidth()];
      }
  }

//Creating the color scale https://github.com/santilland/plotty/blob/master/src/plotty.js
  var cs_def = {positions:[0, 0.25, 0.5, 0.75, 1], colors:["#0571b0", "#92c5de", "#f7f7f7", "#f4a582", "#ca0020"]};
  var canvasColorScale = d3.select("body").append("canvas")
      .attr("width", 256)
      .attr("height", 1)
      .style("display","none");
  var contextColorScale = canvasColorScale.node().getContext("2d");
  var gradient = contextColorScale.createLinearGradient(0, 0, 256, 1);

for (var i = 0; i < cs_def.colors.length; ++i) {
    gradient.addColorStop(cs_def.positions[i], cs_def.colors[i]);
  }
  contextColorScale.fillStyle = gradient;
  contextColorScale.fillRect(0, 0, 256, 1);

var csImageData = contextColorScale.getImageData(0, 0, 255, 1).data;

//Drawing the image
  var canvasRaster = d3.select("body").append("canvas")
      .attr("width", width)
      .attr("height", height)
      .style("display","none");

var contextRaster = canvasRaster.node().getContext("2d");

var id = contextRaster.createImageData(width,height);
  var data = id.data;
  var pos = 0;
  for(var j = 0; j<height; j++){
    for(var i = 0; i<width; i++){
      var pointCoords = projection.invert([i,j]);
      var px = invGeoTransform[0] + pointCoords[0]* invGeoTransform[1];
      var py = invGeoTransform[3] + pointCoords[1] * invGeoTransform[5];

if(Math.floor(px) >= 0 && Math.ceil(px) < image.getWidth() && Math.floor(py) >= 0 && Math.ceil(py) < image.getHeight()){
        //https://en.wikipedia.org/wiki/Bilinear_interpolation
        var value = tempData[Math.floor(py)][Math.floor(px)]*(Math.ceil(px)-px)*(Math.ceil(py)-py)+
        tempData[Math.floor(py)][Math.ceil(px)]*(px-Math.floor(px))*(Math.ceil(py)-py) +
        tempData[Math.ceil(py)][Math.floor(px)]*(Math.ceil(px)-px)*(py-Math.floor(py)) +
        tempData[Math.ceil(py)][Math.ceil(px)]*(px-Math.floor(px))*(py-Math.floor(py));

var c = Math.round(255 * ((value - 14)/24));
        var alpha = 200;
        if (c<0 || c > 255){
          alpha = 0;
        }
        data[pos]   = csImageData[c*4];;
        data[pos+1]   = csImageData[c*4+1];
        data[pos+2]   = csImageData[c*4+2];
        data[pos+3]   = alpha;
        pos = pos + 4
      }
    }
  }
  contextRaster.putImageData( id, 0, 0);
  context.drawImage(canvasRaster.node(), 0, 0);

});
});
</script>

</body>

Modified http://d3js.org/topojson.v1.min.js to a secure url

https://d3js.org/d3.v4.min.js

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

https://d3js.org/d3-scale-chromatic.v1.min.js