feat(geojson): Rect encoding

Author: missinglink

geojson/geometry.ts

@@ -7,10 +7,10 @@ import { Rect } from '../s2/Rect'
 import * as point from './point'
 import * as linestring from './linestring'
 import * as polygon from './polygon'
-import { Loop } from '../s2/Loop'
+import * as rect from './rect'
 
-export type Decodable = Point | Polyline | Polygon | Point[] | Polyline[] | Polygon[]
-export type Encodable = bigint | Cell | Rect | Decodable
+export type Decodable = Point | Polyline | Polygon | Rect | Point[] | Polyline[] | Polygon[]
+export type Encodable = bigint | Cell | Decodable
 
 /**
  * Returns a geojson Geometry given a s2 shape(s).
@@ -19,14 +19,11 @@ export type Encodable = bigint | Cell | Rect | Decodable
 export const toGeoJSON = (shape: Encodable): geojson.Geometry => {
   if (typeof shape === 'bigint') shape = Cell.fromCellID(shape)
   if (shape instanceof Cell) shape = Polygon.fromCell(shape)
-  else if (shape instanceof Rect) {
-    const loop = new Loop(Array(4).map((_, i) => Point.fromLatLng((shape as Rect).vertex(i))))
-    shape = Polygon.fromOrientedLoops([loop])
-  }
 
   if (shape instanceof Point) return point.marshal(shape)
   if (shape instanceof Polyline) return linestring.marshal(shape)
   if (shape instanceof Polygon) return polygon.marshal(shape)
+  if (shape instanceof Rect) return rect.marshal(shape)
 
   if (Array.isArray(shape) && shape.length) {
     if (shape.every((g: any) => g instanceof Point)) return point.marshalMulti(shape as Point[])
@@ -46,7 +43,10 @@ export const fromGeoJSON = (geometry: geojson.Geometry): Decodable => {
 
   if (t === 'Point') return point.unmarshal(geometry as geojson.Point)
   if (t === 'LineString') return linestring.unmarshal(geometry as geojson.LineString)
-  if (t === 'Polygon') return polygon.unmarshal(geometry as geojson.Polygon)
+  if (t === 'Polygon') {
+    if (rect.valid(geometry as geojson.Polygon)) return rect.unmarshal(geometry as geojson.Polygon)
+    return polygon.unmarshal(geometry as geojson.Polygon)
+  }
 
   if (t === 'MultiPoint') return point.unmarshalMulti(geometry as geojson.MultiPoint)
   if (t === 'MultiLineString') return linestring.unmarshalMulti(geometry as geojson.MultiLineString)

geojson/rect.ts

@@ -0,0 +1,56 @@
+import type * as geojson from 'geojson'
+import { Rect } from '../s2/Rect'
+import { Interval as R1Interval } from '../r1/Interval'
+import { Interval as S1Interval } from '../s1/Interval'
+import { Point } from '../s2/Point'
+import { Loop } from '../s2/Loop'
+import { Polygon } from '../s2/Polygon'
+import * as polygon from './polygon'
+import { DEGREE } from '../s1/angle_constants'
+
+/**
+ * Returns a geojson Polygon geometry given an s2 Rect.
+ * @category Constructors
+ */
+export const marshal = (rect: Rect): geojson.Polygon => {
+  const loop = new Loop(Array.from({ length: 4 }, (_, i) => Point.fromLatLng(rect.vertex(i))))
+  return polygon.marshal(Polygon.fromOrientedLoops([loop]))
+}
+
+/**
+ * Constructs an s2 Rect given a geojson Polygon geometry.
+ * @category Constructors
+ */
+export const unmarshal = (geometry: geojson.Polygon): Rect => {
+  const ring = geometry.coordinates[0]
+  const lngLo = Math.min(ring[0][0], ring[2][0])
+  const lngHi = Math.max(ring[0][0], ring[2][0])
+  const latLo = Math.min(ring[0][1], ring[2][1])
+  const latHi = Math.max(ring[0][1], ring[2][1])
+
+  return new Rect(
+    new R1Interval(latLo * DEGREE, latHi * DEGREE),
+    S1Interval.fromEndpoints(lngLo * DEGREE, lngHi * DEGREE)
+  )
+}
+
+/**
+ * Returns true iff the geojson Polygon represents a valid Rect.
+ * @category Constructors
+ */
+export const valid = (geometry: geojson.Polygon): boolean => {
+  if (geometry?.type !== 'Polygon') return false
+  if (geometry?.coordinates.length !== 1) return false
+  const ring = geometry.coordinates[0]
+  if (ring.length !== 5) return false
+  if (!pointsEqual(ring[0], ring[4])) return false
+  if (!lngEqual(ring[0], ring[3])) return false
+  if (!lngEqual(ring[1], ring[2])) return false
+  if (!latEqual(ring[0], ring[1])) return false
+  if (!latEqual(ring[2], ring[3])) return false
+  return true
+}
+
+const lngEqual = (a: geojson.Position, b: geojson.Position) => a[0] === b[0]
+const latEqual = (a: geojson.Position, b: geojson.Position) => a[1] === b[1]
+const pointsEqual = (a: geojson.Position, b: geojson.Position) => lngEqual(a, b) && latEqual(a, b)