add next(), prev(), and other helpers

src/s2geometry.js

@@ -202,7 +202,6 @@ var pointToHilbertQuadList = function(x,y,order) {
   return positions;
 };
 
-
 // S2Cell class
 
 S2.S2Cell = function(){};
@@ -340,10 +339,16 @@ S2.fromFacePosLevel = function (faceN, posS, levelN) {
     bin += '0';
   }
 
-  return Long.fromString(bin, true, 2).toString();
+  return Long.fromString(bin, true, 2).toString(10);
 };
 
-S2.toHilbertQuadkey = function (idS) {
+S2.toId = S2.toCellId = S2.fromKey = function (key) {
+  var parts = key.split('/');
+
+  return S2.fromFacePosLevel(parts[0], parts[1], parts[1].length);
+};
+
+S2.toKey = S2.fromId = S2.fromCellId = S2.toHilbertQuadkey = function (idS) {
   var Long = exports.dcodeIO && exports.dcodeIO.Long || require('long');
   var bin = Long.fromString(idS, true, 10).toString(2);
   var lsbIndex = bin.lastIndexOf('1');
@@ -365,6 +370,61 @@ S2.toHilbertQuadkey = function (idS) {
   return faceS + '/' + posS;
 };
 
+S2.latLngToKey = S2.latLngToQuadkey = function (lat, lng, level) {
+  // TODO
+  //
+  // S2.idToLatLng(id)
+  // S2.keyToLatLng(key)
+  //
+  // .toKeyArray(id)  // face,quadtree
+  // .toKey(id)       // hilbert
+  // .toPoint(id)     // ij
+  // .toId(key)       // uint64 (as string)
+  // .toLong(key)     // long.js
+  // .toLatLng(id)    // object? or array?, or string (with comma)?
+  // maybe S2.HQ.x, S2.GPS.x, S2.CI.x?
+  return S2.S2Cell.FromLatLng({ lat: lat, lng: lng }, level).toHilbertQuadkey();
+};
+
+S2.stepKey = function (key, num) {
+  var Long = exports.dcodeIO && exports.dcodeIO.Long || require('long');
+  var parts = key.split('/');
+
+  var faceS = parts[0];
+  var posS = parts[1];
+  var level = parts[1].length;
+
+  var posL = Long.fromString(posS, true, 4);
+  // TODO handle wrapping (0 === pos + 1)
+  // (only on the 12 edges of the globe)
+  var otherL;
+  if (num > 0) {
+    otherL = posL.add(Math.abs(num));
+  }
+  else if (num < 0) {
+    otherL = posL.subtract(Math.abs(num));
+  }
+  var otherS = otherL.toString(4);
+
+  if ('0' === otherS) {
+    console.warning(new Error("face/position wrapping is not yet supported"));
+  }
+
+  while (otherS.length < level) {
+    otherS = '0' + otherS;
+  }
+
+  return faceS + '/' + otherS;
+};
+
+S2.prevKey = function (key) {
+  return S2.stepKey(key, -1);
+};
+
+S2.nextKey = function (key) {
+  return S2.stepKey(key, 1);
+};
+
 })('undefined' !== typeof window ? window : module.exports);
 
 (function (exports) {

tests/prev-next.js

@@ -0,0 +1,50 @@
+'use strict';
+
+var S2 = require('../src/s2geometry.js').S2;
+
+function getNeighbors(lat, lng, step) {
+    //var step = 10;
+    var level = 15;
+    var origin = S2.latLngToQuadkey(lat, lng, level);
+    var walk = [];
+    // 10 before and 10 after
+    var next = S2.nextKey(origin);
+    var prev = S2.prevKey(origin);
+    var i;
+
+    for (i = 0; i < step; i++) {
+        walk.unshift(S2.toId(prev));
+        prev = S2.prevKey(prev);
+    }
+
+    walk.push(S2.toId(origin));
+
+    for (i = 0; i < step; i++) {
+        // in range(10):
+        walk.push(S2.toId(next));
+        next = S2.nextKey(next);
+    }
+
+    return walk;
+}
+
+
+// Startup Building in Provo
+var lat = 40.2262363;
+var lng = -111.6630927;
+
+var walk = getNeighbors(lat, lng, 5);
+
+walk.forEach(function (cellId, i) {
+  var key = S2.fromId(cellId);
+  var face = parseInt(key.substr(0, 1), 10);
+  var pos = key.substr(2);
+  var level = pos.length;
+
+  // TODO
+  // S2.keyToLatLng(key);
+  // S2.idToLatLng(id);
+
+  // ! because converting CellId / HilbertQuadkey to LatLng is not implemented... yet
+  console.log(-((walk.length - 1) / 2) + i, face, cellId, S2.fromId(cellId), '!', level);
+});