Rewritten tile request calculation

code/map_data.js

@@ -12,34 +12,30 @@ window.requestData = function() {
   requests.abort();
   cleanUp();
 
-  var magic = convertCenterLat(map.getCenter().lat);
-  var R = calculateR(magic);
-
   var bounds = map.getBounds();
-  // convert to point values
+
-  topRight = convertLatLngToPoint(bounds.getNorthEast(), magic, R);
+  var x1 = lngToTile(bounds.getNorthWest().lng, map.getZoom());
-  bottomLeft = convertLatLngToPoint(bounds.getSouthWest() , magic, R);
+  var x2 = lngToTile(bounds.getNorthEast().lng, map.getZoom());
-  // how many quadrants intersect the current view?
+  var y1 = latToTile(bounds.getNorthWest().lat, map.getZoom());
-  quadsX = Math.abs(bottomLeft.x - topRight.x);
+  var y2 = latToTile(bounds.getSouthWest().lat, map.getZoom());
-  quadsY = Math.abs(bottomLeft.y - topRight.y);
 
   // will group requests by second-last quad-key quadrant
   tiles = {};
 
   // walk in x-direction, starts right goes left
-  for(var i = 0; i <= quadsX; i++) {
+  for (var x = x1; x <= x2; x++) {
-    var x = Math.abs(topRight.x - i);
+    for (var y = y1; y <= y2; y++) {
-    var qk = pointToQuadKey(x, topRight.y);
+      var tile_id = pointToTileId(map.getZoom(), x, y);
-    var bnds = convertPointToLatLng(x, topRight.y, magic, R);
+      var bucket = Math.floor(x / 2) + "" + Math.floor(y / 2);
-    if(!tiles[qk.slice(0, -1)]) tiles[qk.slice(0, -1)] = [];
+      if (!tiles[bucket])
-    tiles[qk.slice(0, -1)].push(generateBoundsParams(qk, bnds));
+        tiles[bucket] = [];
-
+      tiles[bucket].push(generateBoundsParams(
-    // walk in y-direction, starts top, goes down
+        tile_id,
-    for(var j = 1; j <= quadsY; j++) {
+        tileToLat(y + 1, map.getZoom()),
-      var qk = pointToQuadKey(x, topRight.y + j);
+        tileToLng(x, map.getZoom()),
-      var bnds = convertPointToLatLng(x, topRight.y + j, magic, R);
+        tileToLat(y, map.getZoom()),
-      if(!tiles[qk.slice(0, -1)]) tiles[qk.slice(0, -1)] = [];
+        tileToLng(x + 1, map.getZoom())
-      tiles[qk.slice(0, -1)].push(generateBoundsParams(qk, bnds));
+      ));
     }
   }
 

code/map_data_calc_tools.js

@@ -1,65 +1,45 @@
-
 // MAP DATA REQUEST CALCULATORS //////////////////////////////////////
 // Ingress Intel splits up requests for map data (portals, links,
 // fields) into tiles. To get data for the current viewport (i.e. what
 // is currently visible) it first calculates which tiles intersect.
 // For all those tiles, it then calculates the lat/lng bounds of that
 // tile and a quadkey. Both the bounds and the quadkey are “somewhat”
-// required to get complete data. No idea how the projection between
+// required to get complete data.
-// lat/lng and tiles works.
+//
-// What follows now are functions that allow conversion between tiles
+// Convertion functions courtesy of
-// and lat/lng as well as calculating the quad key. The variable names
+// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
-// may be misleading.
-// The minified source for this code was in gen_dashboard.js after the
-// “// input 89” line (alternatively: the class was called “Xe”).
 
-window.convertCenterLat = function(centerLat) {
+window.lngToTile = function(lng, zoom) {
-  return Math.round(256 * 0.9999 * Math.abs(1 / Math.cos(centerLat * DEG2RAD)));
+  return Math.floor((lng + 180) / 360 * Math.pow(2, zoom));
 }
 
-window.calculateR = function(convCenterLat) {
+window.latToTile = function(lat, zoom) {
-  return 1 << window.map.getZoom() - (convCenterLat / 256 - 1);
+  return Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180) +
+    1 / Math.cos(lat * Math.PI / 180)) / Math.PI) / 2 * Math.pow(2, zoom));
 }
 
-window.convertLatLngToPoint = function(latlng, magic, R) {
+window.tileToLng = function(x, zoom) {
-  var x = (magic + latlng.lng * magic / 180)*R;
+  return x / Math.pow(2, zoom) * 360 - 180;
-  var l = Math.sin(latlng.lat * DEG2RAD);
-  var y =  (magic + Math.log((1+l)/(1-l)) * -(magic / (2*Math.PI)))*R;
-  return {x: Math.floor(x/magic), y: Math.floor(y/magic)};
 }
 
-window.convertPointToLatLng = function(x, y, magic, R) {
+window.tileToLat = function(y, zoom) {
-  var e = {};
+  var n = Math.PI - 2 * Math.PI * y / Math.pow(2, zoom);
-  e.sw = {
+  return 180 / Math.PI * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n)));
-    // orig function put together from all over the place
-    // lat: (2 * Math.atan(Math.exp((((y + 1) * magic / R) - (magic/ 2)) / (-1*(magic / (2 * Math.PI))))) - Math.PI / 2) / (Math.PI / 180),
-    // shortened version by your favorite algebra program.
-    lat: (360*Math.atan(Math.exp(Math.PI - Math.PI*(y+1)/R)))/Math.PI - 90,
-    lng: 180*x/R-180
-  };
-  e.ne = {
-    //lat: (2 * Math.atan(Math.exp(((y * magic / R) - (magic/ 2)) / (-1*(magic / (2 * Math.PI))))) - Math.PI / 2) / (Math.PI / 180),
-    lat: (360*Math.atan(Math.exp(Math.PI - Math.PI*y/R)))/Math.PI - 90,
-    lng: 180*(x+1)/R-180
-  };
-  return e;
 }
 
-// calculates the quad key for a given point. The point is not(!) in
+window.pointToTileId = function(zoom, x, y) {
-// lat/lng format.
+  return zoom + "_" + x + "_" + y;
-window.pointToQuadKey = function(x, y) {
-  return window.map.getZoom() + "_" + x + "_" + y;
 }
 
-// given quadkey and bounds, returns the format as required by the
+// given tile id and bounds, returns the format as required by the
 // Ingress API to request map data.
-window.generateBoundsParams = function(quadkey, bounds) {
+window.generateBoundsParams = function(tile_id, minLat, minLng, maxLat, maxLng) {
   return {
-    id: quadkey,
+    id: tile_id,
-    qk: quadkey,
+    qk: tile_id,
-    minLatE6: Math.round(bounds.sw.lat * 1E6),
+    minLatE6: Math.round(minLat * 1E6),
-    minLngE6: Math.round(bounds.sw.lng * 1E6),
+    minLngE6: Math.round(minLng * 1E6),
-    maxLatE6: Math.round(bounds.ne.lat * 1E6),
+    maxLatE6: Math.round(maxLat * 1E6),
-    maxLngE6: Math.round(bounds.ne.lng * 1E6)
+    maxLngE6: Math.round(maxLng * 1E6)
   };
 }