From 6ca10b412156f83a1b049c2da4b949b07b478614 Mon Sep 17 00:00:00 2001
From: neocarto <nicolas.lambert@cnrs.fr>
Date: Tue, 3 Dec 2024 13:15:42 +0100
Subject: [PATCH] projections wip

---
 src/projection/hoaxiaoguang.js   | 16 +++++++
 src/projection/polar.js          | 12 +++++
 src/projection/spilhaus.js       | 76 ++++++++++++++++++++++++++++++++
 src/projection/stringtod3proj.js | 20 +++++++++
 4 files changed, 124 insertions(+)
 create mode 100644 src/projection/hoaxiaoguang.js
 create mode 100644 src/projection/polar.js
 create mode 100644 src/projection/spilhaus.js
 create mode 100644 src/projection/stringtod3proj.js

diff --git a/src/projection/hoaxiaoguang.js b/src/projection/hoaxiaoguang.js
new file mode 100644
index 0000000..260983f
--- /dev/null
+++ b/src/projection/hoaxiaoguang.js
@@ -0,0 +1,16 @@
+import { geoHufnagel } from "d3-geo-projection";
+const d3 = Object.assign({}, { geoHufnagel });
+
+// Approximative projection of HoaXiaoguang (thanks to Fil/@recifs)
+
+export function HoaXiaoguang() {
+  const projection = d3
+    .geoHufnagel()
+    .a(0.8)
+    .b(0.35)
+    .psiMax(50)
+    .ratio(1.6)
+    .angle(90)
+    .rotate([110, -200, 90]);
+  return projection;
+}
diff --git a/src/projection/polar.js b/src/projection/polar.js
new file mode 100644
index 0000000..bca327d
--- /dev/null
+++ b/src/projection/polar.js
@@ -0,0 +1,12 @@
+import { geoAzimuthalEquidistant } from "d3-geo";
+const d3 = Object.assign({}, { geoAzimuthalEquidistant });
+
+export function Polar() {
+  const projection = d3
+    .geoAzimuthalEquidistant()
+    .scale(190)
+    .rotate([0, -90])
+    .clipAngle(150);
+
+  return projection;
+}
diff --git a/src/projection/spilhaus.js b/src/projection/spilhaus.js
new file mode 100644
index 0000000..ae2f1bf
--- /dev/null
+++ b/src/projection/spilhaus.js
@@ -0,0 +1,76 @@
+// Thanks to Torben Jansen.
+// See https://observablehq.com/@toja/spilhaus-world-ocean-map-in-a-square
+
+//import * as d3geo from "d3-geo";
+import { geoProjection } from "d3-geo";
+const d3 = Object.assign({}, { geoProjection });
+
+function ellipticF(phi, m) {
+  const { abs, atan, ln, PI: pi, sin, sqrt } = Math;
+  const C1 = 10e-4,
+    C2 = 10e-10,
+    TOL = 10e-6;
+  const sp = sin(phi);
+
+  let k = sqrt(1 - m),
+    h = sp * sp;
+
+  // "complete" elliptic integral
+  if (h >= 1 || abs(phi) === pi / 2) {
+    if (k <= TOL) return sp < 0 ? -Infinity : Infinity;
+    (m = 1), (h = m), (m += k);
+    while (abs(h - k) > C1 * m) {
+      k = sqrt(h * k);
+      (m /= 2), (h = m), (m += k);
+    }
+    return sp < 0 ? -pi / m : pi / m;
+  }
+  // "incomplete" elliptic integral
+  else {
+    if (k <= TOL) return ln((1 + sp) / (1 - sp)) / 2;
+    let g, n, p, r, y;
+    (m = 1), (n = 0), (g = m), (p = m * k), (m += k);
+    y = sqrt((1 - h) / h);
+    if (abs((y -= p / y)) <= 0) y = C2 * sqrt(p);
+    while (abs(g - k) > C1 * g) {
+      (k = 2 * sqrt(p)), (n += n);
+      if (y < 0) n += 1;
+      (p = m * k), (g = m), (m += k);
+      if (abs((y -= p / y)) <= 0) y = C2 * sqrt(p);
+    }
+    if (y < 0) n += 1;
+    r = (atan(m / y) + pi * n) / m;
+    return sp < 0 ? -r : r;
+  }
+}
+
+function ellipticFactory(a, b, sm, sn) {
+  let m = Math.asin(Math.sqrt(1 + Math.min(0, Math.cos(a + b))));
+  if (sm) m = -m;
+
+  let n = Math.asin(Math.sqrt(Math.abs(1 - Math.max(0, Math.cos(a - b)))));
+  if (sn) n = -n;
+
+  return [ellipticF(m, 0.5), ellipticF(n, 0.5)];
+}
+
+//export function Spilhaus() {
+const { abs, max, min, sin, cos, asin, acos, tan } = Math;
+
+function spilhausSquareRaw(lambda, phi) {
+  let a, b, sm, sn, xy;
+  const sp = tan(0.5 * phi);
+  a = cos(asin(sp)) * sin(0.5 * lambda);
+  sm = sp + a < 0;
+  sn = sp - a < 0;
+  b = acos(sp);
+  a = acos(a);
+
+  return ellipticFactory(a, b, sm, sn);
+}
+
+export function Spilhaus() {
+  return d3
+    .geoProjection(spilhausSquareRaw)
+    .rotate([-66.94970198, 49.56371678, 40.17823482]);
+}
diff --git a/src/projection/stringtod3proj.js b/src/projection/stringtod3proj.js
new file mode 100644
index 0000000..d6293e5
--- /dev/null
+++ b/src/projection/stringtod3proj.js
@@ -0,0 +1,20 @@
+import * as d3geo from "d3-geo";
+import * as d3geoprojection from "d3-geo-projection";
+const d3 = Object.assign({}, d3geo, d3geoprojection);
+
+export function stringtod3proj(string) {
+  let str = string;
+  str = str.replace(/\s/g, "");
+
+  if (str.substring(0, 6) !== "d3.geo") {
+    if (str.indexOf(".") === -1) {
+      str += "()";
+    } else {
+      str = str.replace(".", "().");
+    }
+    str = "d3.geo" + str;
+  }
+
+  const createProjection = new Function("d3", `return (${str})`);
+  return createProjection(d3);
+}