feat(geohash, quadkey): New geohash and quadkey modules (#319)

docs/whats-new.md

@@ -27,6 +27,18 @@
 
 ## v3.7 (In Development)
 
+**`@math.gl/geohash`** (NEW)
+
+- New module with math for the GeoHash DGGS (Discrete Global Grid System).
+
+**`@math.gl/s2`** (NEW MODULE)
+
+- New module that contains a lightweight implementation of the S2 DGGS (Discrete Global Grid System).
+
+**`@math.gl/quadkey`** (NEW)
+
+- New module with math for the quadkey DGGS (Discrete Global Grid System).
+
 **`@math.gl/core`
 
 - `config` is now truly global (stored on `globalThis`).
@@ -35,10 +47,6 @@
 
 - Add `isTypedArray()` and `isNumericArray()` utilities that both check values and return properly restricted types to help write strictly typed code (avoids the `DataView` issue with `ArrayBuffer.isView()`).
 
-**`@math.gl/s2`** (NEW MODULE)
-
-- New module that contains a lightweight implementation of the S2 DGGS (Discrete Global Grid System).
-
 ## v3.6
 
 Target Release Date: Q4, 2021

modules/geohash/README.md

@@ -0,0 +1,7 @@
+# @math.gl/sun
+
+[math.gl](https://math.gl/docs) is a suite of math modules for 3D and geospatial applications.
+
+This module contains math for the GeoHash DGGS (Discrete Global Grid System).
+
+For documentation please visit the [website](https://math.gl).

modules/geohash/docs/README.md

@@ -0,0 +1,19 @@
+# Overview
+
+`@math.gl/geohash` is a JavaScript library with 
+
+## Installation
+
+```bash
+npm install @math.gl/sun
+```
+
+## Usage
+
+```js
+import {getGeohashPolygon} from '@math.gl/quadkey';
+const polygon = getGeohashPolygon(geohash);
+```
+
+## Attribution
+

modules/geohash/docs/api-reference/geohash.md

@@ -0,0 +1,3 @@
+# geohash
+
+> TBA

modules/geohash/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "@math.gl/geohash",
+  "description": "Math for the GeoHash DGGS (Discrete Global Grid System)",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "version": "3.6.3",
+  "keywords": [
+    "javascript",
+    "math",
+    "geospatial",
+    "sun",
+    "suncalc",
+    "solar"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/uber-web/math.gl.git"
+  },
+  "types": "dist/index.d.ts",
+  "main": "dist/es5/index.js",
+  "module": "dist/esm/index.js",
+  "files": [
+    "dist",
+    "src"
+  ],
+  "dependencies": {
+    "@babel/runtime": "^7.12.0"
+  }
+}

modules/geohash/src/geohash.ts

@@ -0,0 +1,58 @@
+// math.gl, MIT license
+
+/* eslint-disable max-depth */
+
+const BASE32_CODES = '0123456789bcdefghjkmnpqrstuvwxyz';
+const BASE32_CODES_DICT: Record<string, number> = {};
+for (let i = 0; i < BASE32_CODES.length; i++) {
+  BASE32_CODES_DICT[BASE32_CODES.charAt(i)] = i;
+}
+
+const MIN_LAT = -90;
+const MAX_LAT = 90;
+const MIN_LON = -180;
+const MAX_LON = 180;
+
+// Adapted from ngeohash decode_bbox
+export function getGeohashBounds(geohash: string): number[] {
+  let isLon = true;
+  let maxLat = MAX_LAT;
+  let minLat = MIN_LAT;
+  let maxLon = MAX_LON;
+  let minLon = MIN_LON;
+  let mid: number;
+
+  let hashValue = 0;
+  for (let i = 0, l = geohash.length; i < l; i++) {
+    const code = geohash[i].toLowerCase();
+    hashValue = BASE32_CODES_DICT[code];
+
+    for (let bits = 4; bits >= 0; bits--) {
+      const bit = (hashValue >> bits) & 1;
+      if (isLon) {
+        mid = (maxLon + minLon) / 2;
+        if (bit === 1) {
+          minLon = mid;
+        } else {
+          maxLon = mid;
+        }
+      } else {
+        mid = (maxLat + minLat) / 2;
+        if (bit === 1) {
+          minLat = mid;
+        } else {
+          maxLat = mid;
+        }
+      }
+      isLon = !isLon;
+    }
+  }
+
+  return [minLat, minLon, maxLat, maxLon];
+}
+
+export function getGeohashPolygon(geohash: string): number[] {
+  const [s, w, n, e] = getGeohashBounds(geohash);
+
+  return [e, n, e, s, w, s, w, n, e, n];
+}

modules/geohash/src/index.ts

@@ -0,0 +1 @@
+export {getGeohashBounds, getGeohashPolygon} from './geohash';