Add quadbinToBoundary utility

CONTRIBUTING.md

@@ -0,0 +1,24 @@
+## Quickstart
+
+To install and build `quadbin-js` locally from source:
+
+```bash
+# install dependencies
+yarn
+
+# build package once
+yarn build
+```
+
+To run tests, coverage, or a linter, you should execute `yarn build`, and afterward:
+
+```bash
+# run tests once
+yarn test
+```
+
+## Releases
+
+1. Create a new version: `yarn version [ major | minor | patch | prerelease ]`
+
+2. Execute `yarn publish`

README.md

@@ -79,4 +79,10 @@ Converts quadbin cell into a xyz tile.
 function geometryToCells(geometry: GeoJSONGeometry, resolution: bigint): bigint 
 ```
 
-Returns a list of cells covering a GeoJSON geometry at a given resolution
+## cellToBoundary
+
+```javascript
+function cellToBoundary(quadbin: bigint): GeoJSONGeometry 
+```
+
+Converts a Quadbin cell identifier into a geographical boundary represented as a polygon

package.json

@@ -32,20 +32,23 @@
     "build:esm": "tsc -p tsconfig/tsconfig.esm.json",
     "build:types": "tsc -p tsconfig/tsconfig.types.json",
     "build:umd": "webpack --config tsconfig/webpack.config.cjs",
-    "lint": "npx prettier --check src",
+    "lint": "prettier --check src",
     "test": "yarn lint && yarn test-fast",
-    "test-fast": "npx ts-node node_modules/tape/bin/tape test/**/*.spec.js"
+    "test-fast": "ts-node node_modules/tape/bin/tape test/**/*.spec.js",
+    "prepublishOnly": "yarn build"
   },
   "browser": {
     "jsdom": false
   },
   "devDependencies": {
     "@babel/register": "^7.13.0",
+    "@types/geojson": "^7946.0.14",
     "babel-loader": "^8.0.0",
     "babel-preset-minify": "^0.5.0",
     "prettier": "^2.4.1",
     "tape": "^5.3.0",
     "ts-loader": "^9.2.5",
+    "ts-node": "^10.9.2",
     "typescript": "^4.4.4",
     "webpack": "^5.52.1",
     "webpack-cli": "^4.8.0"
@@ -54,6 +57,12 @@
     "node": ">=14"
   },
   "dependencies": {
-    "@mapbox/tile-cover": "3.0.1"
+    "@mapbox/tile-cover": "3.0.1",
+    "@math.gl/web-mercator": "^4.1.0"
+  },
+  "packageManager": "[email protected]",
+  "volta": {
+    "node": "14.21.3",
+    "yarn": "1.22.22"
   }
 }

src/index.ts

@@ -1,4 +1,6 @@
 import {tiles} from '@mapbox/tile-cover';
+import {worldToLngLat} from '@math.gl/web-mercator';
+import type {Polygon} from 'geojson';
 
 const B = [
   0x5555555555555555n,
@@ -13,6 +15,29 @@ const S = [0n, 1n, 2n, 4n, 8n, 16n];
 type Quadbin = bigint;
 type Tile = {x: number; y: number; z: number};
 
+const TILE_SIZE = 512;
+
+function quadbinToOffset(quadbin: bigint): [number, number, number] {
+  const {x, y, z} = cellToTile(quadbin);
+  const scale = TILE_SIZE / (1 << z);
+  return [x * scale, TILE_SIZE - y * scale, scale];
+}
+
+function quadbinToWorldBounds(quadbin: bigint, coverage: number): [number[], number[]] {
+  const [xOffset, yOffset, scale] = quadbinToOffset(quadbin);
+  return [
+    [xOffset, yOffset],
+    [xOffset + coverage * scale, yOffset - coverage * scale]
+  ];
+}
+
+function getQuadbinPolygon(quadbin: bigint, coverage = 1): number[] {
+  const [topLeft, bottomRight] = quadbinToWorldBounds(quadbin, coverage);
+  const [w, n] = worldToLngLat(topLeft);
+  const [e, s] = worldToLngLat(bottomRight);
+  return [e, n, e, s, w, s, w, n, e, n];
+}
+
 export function hexToBigInt(hex: string): bigint {
   return BigInt(`0x${hex}`);
 }
@@ -89,3 +114,16 @@ export function geometryToCells(geometry, resolution: bigint): Quadbin[] {
     max_zoom: zoom
   }).map(([x, y, z]) => tileToCell({x, y, z}));
 }
+
+export function cellToBoundary(cell: bigint): Polygon {
+  const bbox = getQuadbinPolygon(cell);
+  const boundary = [
+    [bbox[0], bbox[1]],
+    [bbox[2], bbox[3]],
+    [bbox[4], bbox[5]],
+    [bbox[6], bbox[7]],
+    [bbox[0], bbox[1]]
+  ];
+
+  return {type: 'Polygon', coordinates: [boundary]};
+}

test/index.spec.js

@@ -5,7 +5,7 @@ import {
   cellToParent,
   geometryToCells,
   getResolution,
-  hexToBigInt
+  cellToBoundary
 } from 'quadbin';
 
 import {tileToQuadkey} from './quadkey-utils.js';
@@ -16,6 +16,8 @@ const TEST_TILES = [
   {x: 1023, y: 2412, z: 23, q: 5291729562728627583n}
 ];
 
+const ANY_QUADBIN = BigInt(524800);
+
 test('Quadbin conversion', async t => {
   for (const {x, y, z, q} of TEST_TILES) {
     const tile = {x, y, z};
@@ -51,7 +53,6 @@ test('Quadbin getParent', async t => {
 import PointGeometry from './data/PointGeometry.json' assert {type: 'json'};
 import MultiPointGeometry from './data/MultiPointGeometry.json' assert {type: 'json'};
 import LineStringGeometry from './data/LineStringGeometry.json' assert {type: 'json'};
-import MultiLineStringGeometry from './data/MultiLineStringGeometry.json' assert {type: 'json'};
 import PolygonGeometry from './data/PolygonGeometry.json' assert {type: 'json'};
 import PolygonAntimeridianGeometry from './data/PolygonAntimeridianGeometry.json' assert {type: 'json'};
 import MultiPolygonGeometry from './data/MultiPolygonGeometry.json' assert {type: 'json'};
@@ -78,3 +79,58 @@ test('Quadbin geometryToCells', async t => {
   }
   t.end();
 });
+
+test('Quadbin cellToBoundary', t => {
+  for (const {quadbin, expectedPolygon} of [
+    {
+      quadbin: BigInt(524800),
+      expectedPolygon: {
+        type: 'Polygon',
+        coordinates: [
+          [
+            [180, 85.0511287798066],
+            [180, -85.05112877980659],
+            [-180, -85.05112877980659],
+            [-180, 85.0511287798066],
+            [180, 85.0511287798066]
+          ]
+        ]
+      }
+    },
+    {
+      quadbin: BigInt(536903670), // Longitude near +180°
+      expectedPolygon: {
+        type: 'Polygon',
+        coordinates: [
+          [
+            [180, 85.0511287798066],
+            [180, -85.05112877980659],
+            [-180, -85.05112877980659],
+            [-180, 85.0511287798066],
+            [180, 85.0511287798066]
+          ]
+        ]
+      }
+    },
+    {
+      quadbin: BigInt(536870921), // Longitude near -180°
+      expectedPolygon: {
+        type: 'Polygon',
+        coordinates: [
+          [
+            [180, 85.0511287798066],
+            [180, -85.05112877980659],
+            [-180, -85.05112877980659],
+            [-180, 85.0511287798066],
+            [180, 85.0511287798066]
+          ]
+        ]
+      }
+    }
+  ]) {
+    const result = cellToBoundary(quadbin);
+    t.deepEquals(result, expectedPolygon);
+  }
+
+  t.end();
+});