Reprojected Raster Clipping

This bl.ock takes an alternative approach to this one, in that it is not dependent on a circular projection disc.

It runs each pixel through a forward then inverse projection to see if the pixel should be plotted. It is in response to a SO question, [this was a potential answer] (http://stackoverflow.com/a/41856996/7106086). This is required in transforming the equiratangular source image 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.v3.min.js"></script>
<script src="https://d3js.org/d3.geo.projection.v0.min.js"></script>
<script>

var width = 960,
		height = 500;
/*
	var projection = d3.geoAzimuthalEquidistant()
		.scale(65)
		.precision(.1);
*/

var projection = d3.geo.projection(d3.geo.hammer.raw(1.75, 2))
    .rotate([-10, -45])
    .scale(130)
    .translate([width / 2, height / 2])
    .precision(.1);

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];
			
			var pxy = projection(p);
			
			var tolerance = 0.5;
				
			if ( λ > 180 || λ < -180 || φ > 90 || φ < -90 ) { i += 4; continue; }
			if ( (Math.abs(pxy[0] - x) < tolerance ) && (Math.abs(pxy[1] - y) < tolerance ) ) {

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 {
				i += 4;
			} 
		}
	}

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

}

</script>

https://d3js.org/d3.v3.min.js

https://d3js.org/d3.geo.projection.v0.min.js