Sha256: 08f0080677463bbcff5e58d9301c4812475493aa6ce5f160e53d7433f9e88f9a
Contents?: true
Size: 1.88 KB
Versions: 3
Compression:
Stored size: 1.88 KB
Contents
var healpixParallel = 41 + 48 / 36 + 37 / 3600; // TODO automate
function healpix(h) {
var lambert = d3.geo.cylindricalEqualArea.raw(0),
φ0 = healpixParallel * π / 180,
dx0 = lambert(π, 0)[0] - lambert(-π, 0)[0],
dx1 = d3.geo.collignon.raw(π, φ0)[0] - d3.geo.collignon.raw(-π, φ0)[0],
y0 = lambert(0, φ0)[1],
y1 = d3.geo.collignon.raw(0, φ0)[1],
dy1 = d3.geo.collignon.raw(0, π / 2)[1] - y1,
k = 2 * π / h;
return function(λ, φ) {
var point;
if (Math.abs(φ) > φ0) {
var i = Math.min(h - 1, Math.max(0, Math.floor((λ + π) / k)));
λ = λ + π * (h - 1) / h - i * k;
point = d3.geo.collignon.raw(λ, Math.abs(φ));
point[0] = point[0] * dx0 / dx1 - dx0 * (h - 1) / (2 * h) + i * dx0 / h;
point[1] = y0 + (point[1] - y1) * 4 * dy1 / dx0;
if (φ < 0) point[1] = -point[1];
} else {
point = lambert(λ, φ);
}
point[0] /= 2;
return point;
};
}
function healpixProjection() {
var n = 2,
m = projectionMutator(healpix),
p = m(n),
stream_ = p.stream;
p.lobes = function(_) {
if (!arguments.length) return n;
return m(n = +_);
};
p.stream = function(stream) {
var rotate = p.rotate(),
rotateStream = stream_(stream),
sphereStream = (p.rotate([0, 0]), stream_(stream));
p.rotate(rotate);
rotateStream.sphere = function() { d3.geo.stream(sphere(), sphereStream); };
return rotateStream;
};
function sphere() {
var step = 180 / n;
return {
type: "Polygon",
coordinates: [
d3.range(-180, 180 + step / 2, step).map(function(x, i) { return [x, i & 1 ? 90 - 1e-6 : healpixParallel]; })
.concat(d3.range(180, -180 - step / 2, -step).map(function(x, i) { return [x, i & 1 ? -90 + 1e-6 : -healpixParallel]; }))
]
};
}
return p;
}
(d3.geo.healpix = healpixProjection).raw = healpix;
Version data entries
3 entries across 3 versions & 1 rubygems