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fix albers edge cases and lambert center (#11229)
* fix albers edge cases and lambert center The albers implementation was not solid. Switch to one based on d3-geo (thanks!) which is much more robust. Lambert was not using the center longitude. * bring back albers wrap correction Co-authored-by: Vladimir Agafonkin <[email protected]>
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5 files changed

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‎src/geo/projection/albers.js‎

Lines changed: 29 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -13,47 +13,50 @@ export default {
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conic: true,
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16+
// based on https://github.com/d3/d3-geo-projection, MIT-licensed
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initializeConstants() {
1719
if (this.constants && vec2.exactEquals(this.parallels, this.constants.parallels)) {
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return;
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}
2022

21-
const p1 = degToRad(this.parallels[0]);
22-
const p2 = degToRad(this.parallels[1]);
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const sinp1 = Math.sin(p1);
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const cosp1 = Math.cos(p1);
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const cosp12 = cosp1 * cosp1;
26-
const r = 0.5;
27-
const n = 0.5 * (sinp1 + Math.sin(p2));
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const c = cosp12 + 2 * n * sinp1;
29-
const b = r / n * Math.sqrt(c);
30-
31-
this.constants = {n, b, c, parallels: this.parallels};
23+
const sy0 = Math.sin(degToRad(this.parallels[0]));
24+
const n = (sy0 + Math.sin(degToRad(this.parallels[1]))) / 2;
25+
const c = 1 + sy0 * (2 * n - sy0);
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const r0 = Math.sqrt(c) / n;
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this.constants = {n, c, r0, parallels: this.parallels};
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},
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project(lng: number, lat: number) {
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this.initializeConstants();
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36-
const {n, b, c} = this.constants;
37-
const theta = n * degToRad(lng - this.center[0]);
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const a = 0.5 / n * Math.sqrt(c - 2 * n * Math.sin(degToRad(lat)));
39-
const x = a * Math.sin(theta);
40-
const y = b - a * Math.cos(theta);
34+
const lambda = degToRad(lng - this.center[0]);
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const phi = degToRad(lat);
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42-
return {x: 1 + 0.5 * x, y: 1 - 0.5 * y};
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const {n, c, r0} = this.constants;
38+
const r = Math.sqrt(c - 2 * n * Math.sin(phi)) / n;
39+
const x = r * Math.sin(lambda * n);
40+
const y = r * Math.cos(lambda * n) - r0;
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return {x, y};
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},
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unproject(x: number, y: number) {
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this.initializeConstants();
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const {n, c, r0} = this.constants;
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47-
const {n, b, c} = this.constants;
48-
const x_ = (x - 1) * 2;
49-
const y_ = (y - 1) * -2;
50-
const y2 = -(y_ - b);
48+
const r0y = r0 + y;
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let l = Math.atan2(x, Math.abs(r0y)) * Math.sign(r0y);
50+
if (r0y * n < 0) {
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l -= Math.PI * Math.sign(x) * Math.sign(r0y);
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}
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const dt = degToRad(this.center[0]) * n;
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const theta = wrap(Math.atan2(x_, y2), -Math.PI - dt, Math.PI - dt);
53-
const lng = radToDeg(theta / n) + this.center[0];
54-
const a = x_ / Math.sin(theta);
55-
const s = clamp((Math.pow(a / 0.5 * n, 2) - c) / (-2 * n), -1, 1);
56-
const lat = clamp(radToDeg(Math.asin(s)), -MAX_MERCATOR_LATITUDE, MAX_MERCATOR_LATITUDE);
54+
l = wrap(l, -Math.PI - dt, Math.PI - dt);
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56+
const lng = radToDeg(l / n) + this.center[0];
57+
const phi = Math.asin(clamp((c - (x * x + r0y * r0y) * n * n) / (2 * n), -1, 1));
58+
const lat = clamp(radToDeg(phi), -MAX_MERCATOR_LATITUDE, MAX_MERCATOR_LATITUDE);
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return new LngLat(lng, lat);
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}
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};

‎src/geo/projection/cylindrical_equal_area.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4,7 +4,7 @@ import {clamp, degToRad, radToDeg} from '../../util/util.js';
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import {MAX_MERCATOR_LATITUDE} from '../mercator_coordinate.js';
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export default function(phi: number) {
7-
const cosPhi = Math.cos(degToRad(phi));
7+
const cosPhi = Math.max(0.01, Math.cos(degToRad(phi)));
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// scale coordinates between 0 and 1 to avoid constraint issues
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const scale = 1 / (2 * Math.max(Math.PI * cosPhi, 1 / cosPhi));
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‎src/geo/projection/lambert.js‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -38,7 +38,7 @@ export default {
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// based on https://github.com/d3/d3-geo, MIT-licensed
4040
lat = degToRad(lat);
41-
lng = degToRad(lng);
41+
lng = degToRad(lng - this.center[0]);
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4343
const epsilon = 1e-6;
4444
const {n, f} = this.constants;
@@ -73,7 +73,7 @@ export default {
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7474
if (fy * n < 0) l -= Math.PI * Math.sign(x) * signFy;
7575

76-
const lng = clamp(radToDeg(l / n), -180, 180);
76+
const lng = clamp(radToDeg(l / n) + this.center[0], -180, 180);
7777
const phi = 2 * Math.atan(Math.pow(f / r, 1 / n)) - halfPi;
7878
const lat = clamp(radToDeg(phi), -MAX_MERCATOR_LATITUDE, MAX_MERCATOR_LATITUDE);
7979

‎test/integration/render-tests/map-projections/lambert/configured/expected.png‎

349 Bytes
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‎test/integration/render-tests/video/projected/expected.png‎

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