Azimuthal Equidistant Raster Reprojection

This bl.ock is a response to a question on reprojecting rasters in d3. The approach is covered in this answer: Stack Overflow answer.

It assumes a geographic projection that projects the earth on to a disc, so that one can calculate the radius of the disc and trim the image to this area. This is required as the d3 projection function is not one to one.

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

body {
   background: #222;
}

</style>
<body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var width = 960,
		height = 500;

var projection = d3.geoAzimuthalEquidistant()
		.scale(65)
		.precision(.1);

var edge = {};
	var center = {};

edge.x = projection([180 - 1e-6, 0])[0];
	edge.y = projection([180 - 1e-6, 0])[1];
	
	center.x = width/2;
	center.y = height/2;

var radius = Math.pow( Math.pow(center.x - edge.x,2) + Math.pow(center.y - edge.y,2) , 0.5 )

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

var context = canvas.node().getContext("2d");

var image = new Image;
	image.onload = onload;
	image.src = "readme-blue-marble.jpg";

function onload() {
		var dx = image.width,
		dy = image.height;

context.drawImage(image, 0, 0, dx, dy);

var sourceData = context.getImageData(0, 0, dx, dy).data,
		  target = context.createImageData(width, height),
		  targetData = target.data;

for (var y = 0, i = -1; y < height; ++y) {
			for (var x = 0; x < width; ++x) {
		
			var p = projection.invert([x, y]), λ = p[0], φ = p[1];

if (Math.pow( Math.pow(center.x-x,2) + Math.pow(center.y-y,2), 0.5) < radius) {
				
					if ( λ > 180 || λ < -180 || φ > 90 || φ < -90 ) { i += 4; continue; }
						var q = ((90 - φ) / 180 * dy | 0) * dx + ((180 + λ) / 360 * dx | 0) << 2;
						targetData[++i] = sourceData[q];
						targetData[++i] = sourceData[++q];
						targetData[++i] = sourceData[++q];
						targetData[++i] = 255;
				}
				else {
					targetData[++i] = 0;
					targetData[++i] = 0;
					targetData[++i] = 0;
					targetData[++i] = 0;
				}
			}
		}

context.clearRect(0, 0, width, height);
	  context.putImageData(target, 0, 0);

}

</script>

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