54 lines
1.3 KiB
JavaScript
54 lines
1.3 KiB
JavaScript
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import {Adder} from "d3-array";
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import {abs, atan2, cos, radians, sin, sqrt} from "./math.js";
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import noop from "./noop.js";
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import stream from "./stream.js";
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var lengthSum,
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lambda0,
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sinPhi0,
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cosPhi0;
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var lengthStream = {
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sphere: noop,
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point: noop,
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lineStart: lengthLineStart,
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lineEnd: noop,
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polygonStart: noop,
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polygonEnd: noop
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};
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function lengthLineStart() {
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lengthStream.point = lengthPointFirst;
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lengthStream.lineEnd = lengthLineEnd;
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}
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function lengthLineEnd() {
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lengthStream.point = lengthStream.lineEnd = noop;
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}
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function lengthPointFirst(lambda, phi) {
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lambda *= radians, phi *= radians;
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lambda0 = lambda, sinPhi0 = sin(phi), cosPhi0 = cos(phi);
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lengthStream.point = lengthPoint;
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}
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function lengthPoint(lambda, phi) {
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lambda *= radians, phi *= radians;
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var sinPhi = sin(phi),
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cosPhi = cos(phi),
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delta = abs(lambda - lambda0),
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cosDelta = cos(delta),
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sinDelta = sin(delta),
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x = cosPhi * sinDelta,
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y = cosPhi0 * sinPhi - sinPhi0 * cosPhi * cosDelta,
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z = sinPhi0 * sinPhi + cosPhi0 * cosPhi * cosDelta;
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lengthSum.add(atan2(sqrt(x * x + y * y), z));
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lambda0 = lambda, sinPhi0 = sinPhi, cosPhi0 = cosPhi;
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}
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export default function(object) {
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lengthSum = new Adder();
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stream(object, lengthStream);
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return +lengthSum;
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}
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