You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
77 lines
2.6 KiB
77 lines
2.6 KiB
import {geoProjectionMutator as projectionMutator, geoAzimuthalEquidistantRaw as azimuthalEquidistantRaw} from "d3-geo";
|
|
import {abs, acos, asin, atan, atan2, cos, degrees, halfPi, pi, radians, round, sin, sqrt, tan} from "./math.js";
|
|
|
|
export function berghausRaw(lobes) {
|
|
var k = 2 * pi / lobes;
|
|
|
|
function forward(lambda, phi) {
|
|
var p = azimuthalEquidistantRaw(lambda, phi);
|
|
if (abs(lambda) > halfPi) { // back hemisphere
|
|
var theta = atan2(p[1], p[0]),
|
|
r = sqrt(p[0] * p[0] + p[1] * p[1]),
|
|
theta0 = k * round((theta - halfPi) / k) + halfPi,
|
|
alpha = atan2(sin(theta -= theta0), 2 - cos(theta)); // angle relative to lobe end
|
|
theta = theta0 + asin(pi / r * sin(alpha)) - alpha;
|
|
p[0] = r * cos(theta);
|
|
p[1] = r * sin(theta);
|
|
}
|
|
return p;
|
|
}
|
|
|
|
forward.invert = function(x, y) {
|
|
var r = sqrt(x * x + y * y);
|
|
if (r > halfPi) {
|
|
var theta = atan2(y, x),
|
|
theta0 = k * round((theta - halfPi) / k) + halfPi,
|
|
s = theta > theta0 ? -1 : 1,
|
|
A = r * cos(theta0 - theta),
|
|
cotAlpha = 1 / tan(s * acos((A - pi) / sqrt(pi * (pi - 2 * A) + r * r)));
|
|
theta = theta0 + 2 * atan((cotAlpha + s * sqrt(cotAlpha * cotAlpha - 3)) / 3);
|
|
x = r * cos(theta), y = r * sin(theta);
|
|
}
|
|
return azimuthalEquidistantRaw.invert(x, y);
|
|
};
|
|
|
|
return forward;
|
|
}
|
|
|
|
export default function() {
|
|
var lobes = 5,
|
|
m = projectionMutator(berghausRaw),
|
|
p = m(lobes),
|
|
projectionStream = p.stream,
|
|
epsilon = 1e-2,
|
|
cr = -cos(epsilon * radians),
|
|
sr = sin(epsilon * radians);
|
|
|
|
p.lobes = function(_) {
|
|
return arguments.length ? m(lobes = +_) : lobes;
|
|
};
|
|
|
|
p.stream = function(stream) {
|
|
var rotate = p.rotate(),
|
|
rotateStream = projectionStream(stream),
|
|
sphereStream = (p.rotate([0, 0]), projectionStream(stream));
|
|
p.rotate(rotate);
|
|
rotateStream.sphere = function() {
|
|
sphereStream.polygonStart(), sphereStream.lineStart();
|
|
for (var i = 0, delta = 360 / lobes, delta0 = 2 * pi / lobes, phi = 90 - 180 / lobes, phi0 = halfPi; i < lobes; ++i, phi -= delta, phi0 -= delta0) {
|
|
sphereStream.point(atan2(sr * cos(phi0), cr) * degrees, asin(sr * sin(phi0)) * degrees);
|
|
if (phi < -90) {
|
|
sphereStream.point(-90, -180 - phi - epsilon);
|
|
sphereStream.point(-90, -180 - phi + epsilon);
|
|
} else {
|
|
sphereStream.point(90, phi + epsilon);
|
|
sphereStream.point(90, phi - epsilon);
|
|
}
|
|
}
|
|
sphereStream.lineEnd(), sphereStream.polygonEnd();
|
|
};
|
|
return rotateStream;
|
|
};
|
|
|
|
return p
|
|
.scale(87.8076)
|
|
.center([0, 17.1875])
|
|
.clipAngle(180 - 1e-3);
|
|
}
|
|
|