48 lines
1.1 KiB
JavaScript
48 lines
1.1 KiB
JavaScript
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import {geoProjectionMutator as projectionMutator} from "d3-geo";
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import {abs, asin, atan2, cos, epsilon, halfPi, pow, sign, sin} from "./math";
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export function lagrangeRaw(n) {
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function forward(lambda, phi) {
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if (abs(abs(phi) - halfPi) < epsilon) return [0, phi < 0 ? -2 : 2];
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var sinPhi = sin(phi),
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v = pow((1 + sinPhi) / (1 - sinPhi), n / 2),
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c = 0.5 * (v + 1 / v) + cos(lambda *= n);
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return [
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2 * sin(lambda) / c,
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(v - 1 / v) / c
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];
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}
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forward.invert = function(x, y) {
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var y0 = abs(y);
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if (abs(y0 - 2) < epsilon) return x ? null : [0, sign(y) * halfPi];
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if (y0 > 2) return null;
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x /= 2, y /= 2;
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var x2 = x * x,
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y2 = y * y,
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t = 2 * y / (1 + x2 + y2); // tanh(nPhi)
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t = pow((1 + t) / (1 - t), 1 / n);
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return [
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atan2(2 * x, 1 - x2 - y2) / n,
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asin((t - 1) / (t + 1))
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];
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};
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return forward;
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}
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export default function() {
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var n = 0.5,
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m = projectionMutator(lagrangeRaw),
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p = m(n);
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p.spacing = function(_) {
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return arguments.length ? m(n = +_) : n;
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};
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return p
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.scale(124.75);
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}
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