Skip to content

Instantly share code, notes, and snippets.

@mbostock

mbostock/.block

Forked from jasondavies/README.md
Last active May 10, 2022 12:50
Show Gist options
  • Save mbostock/4329423 to your computer and use it in GitHub Desktop.
Save mbostock/4329423 to your computer and use it in GitHub Desktop.
Download ZIP
Raster Reprojection
Raw
.block
license: gpl-3.0
redirect: https://observablehq.com/@mbostock/raster-reprojection-ii
Raw
README.md
Raw
index.html
<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
background: #222;
}
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/d3.geo.projection.v0.min.js"></script>
<script>
var width = 960,
height = 500;
var projection = d3.geo.kavrayskiy7();
var path = d3.geo.path()
.projection(projection);
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 (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;
}
}
context.clearRect(0, 0, width, height);
context.putImageData(target, 0, 0);
}
</script>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment