Wind barbs from a projected GeoTIFF & JavaScript libraries

This example is the same as this block, but using the original GeoTIFF, ehich is in the Lambert conic conformal projection. Since the GeoJSON and coordinates needed by d3 to draw the map are in WGS84 (longitude-latitude) projection, all the data must be reprojected before drawing it. You can see here how to do it for polygons (the coloured isobands) and points (for wind barbs).

The results are more or less the same as in the previous pre-reprojected example, but should be better, since the isobands and barbs are created from the original data, not interpolated as in the other case.

Several liraries have been used:

geotiff: Reading the GeoTIFF data (not the projectiopn, which would be cool)
proj4js: Reprojecting points
d3-marching-squares: Creating the isobands with the wind speed
reproject: Reprojecting the generated GeoJSON

reproject doesn't ork directly with the browser, so an operation with browserify is needed before doing it:

npm install reproject
cd node_modules/reproject
browserify index.js --standalone reproject > ../../reproject.js

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

</style>
<body>

var projection = d3.geoConicConformal()
    .rotate([82, 0])
    .center([0, 34.83158])
    .parallels([30, 60])
    .scale(2300)
    .translate([width / 2, height / 2]);

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

var context = canvas.node().getContext("2d");
d3.request("wrf_lambert.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 uData = new Array(image.getHeight());
  var vData = new Array(image.getHeight());
  var spdData = new Array(image.getHeight());
  for (var j = 0; j<image.getHeight(); j++){
      uData[j] = new Array(image.getWidth());
      vData[j] = new Array(image.getWidth());
      spdData[j] = new Array(image.getWidth());
      for (var i = 0; i<image.getWidth(); i++){
          uData[j][i] = rasters[0][i + j*image.getWidth()];
          vData[j][i] = rasters[1][i + j*image.getWidth()];
          spdData[j][i] = 1.943844492 * Math.sqrt(uData[j][i]*uData[j][i] + vData[j][i]*vData[j][i]);
      }
  }

var intervalsSpd = [0, 5, 10, 15, 20, 25, 30, 35, 40];
  var bandsSpd = rastertools.isobands(spdData, geoTransform, intervalsSpd);
  //console.info(image.getGeoKeys());
  var firstProjection='PROJCS["unnamed",\
    GEOGCS["unnamed ellipse",\
        DATUM["unknown",\
            SPHEROID["unnamed",6370997,0]],\
        PRIMEM["Greenwich",0],\
        UNIT["degree",0.0174532925199433]],\
    PROJECTION["Lambert_Conformal_Conic_2SP"],\
    PARAMETER["standard_parallel_1",30],\
    PARAMETER["standard_parallel_2",60],\
    PARAMETER["latitude_of_origin",34.83158],\
    PARAMETER["central_meridian",-98],\
    PARAMETER["false_easting",0],\
    PARAMETER["false_northing",0],\
    UNIT["metre",1,\
        AUTHORITY["EPSG","9001"]]]';

bandsSpd = reproject.toWgs84(bandsSpd, firstProjection);
  var colorScale = d3.scaleSequential(d3.interpolateBuPu);
  bandsSpd.features.forEach(function(d, i) {
      context.beginPath();
      context.globalAlpha = 0.7;
      context.fillStyle = colorScale(intervalsSpd[i]/40);
      path(d);
      context.fill();
  });

var xPos = d3.range(barbSize, width, barbSize);
  var yPos = d3.range(barbSize, height, barbSize);

xPos.forEach(function(x){
    yPos.forEach(function(y){
      var coords = projection.invert([x,y]);
      coords = proj4(firstProjection).forward(coords);
      var px = Math.round((coords[0] - geoTransform[0]) / geoTransform[1]);
      var py = Math.round((coords[1] - geoTransform[3]) / geoTransform[5]);
      var angle = Math.atan2(vData[py][px],uData[py][px]);
      var spd5 = Math.round(spdData[py][px]/5);
      var spd10 = Math.floor(spd5/2);
      spd5 = spd5%2;
      var spd50 = Math.floor(spd10/5);
      spd10 = spd10%5;
      context.save();
      context.translate(x, y);
      context.rotate(angle);
      context.beginPath();
      context.strokeStyle = "#444";
      context.fillStyle = "#444";

var pos = -barbSize/2;
      var separation = 3;

for(var i=0; i<spd50; i++){
        context.moveTo(pos, 0);
        context.lineTo(pos+barbSize/8, barbSize/4);
        context.lineTo(pos+barbSize/4, 0);
        pos = pos + barbSize/4 + separation;
        context.fill();
      }
      for(var i=0; i<spd10; i++){
        context.moveTo(pos, 0);
        context.lineTo(pos, barbSize/3);
        pos = pos + separation
      }
      if(spd5==1){
        if (pos == -barbSize/2){
          pos = pos + separation
        }
        context.moveTo(pos, 0);
        context.lineTo(pos, barbSize/6);
      }
      if(spd5==0 && spd10== 0 && spd50==0){
        context.arc(0, 0, 4, 0, 2 * Math.PI, false);
      } else {
        context.moveTo(-barbSize/2,0);
        context.lineTo(barbSize/2,0);
      }
      context.stroke();
      context.restore();
    });
  });

});
});
</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