From ca76e7ed6031259b619969e7906bfe05266adf8e Mon Sep 17 00:00:00 2001
From: Jon Atkins <github@jonatkins.com>
Date: Fri, 17 May 2013 23:45:14 +0100
Subject: [PATCH] add the concept of portal detail level zoom, separate from
 map level zoom

this allows us to override the zoom used to retrieve server data, giving options to either retrieve lower zoom levels to reduce the number of requests, or higher zoom levels to retrieve lower level portals from the server
---
 code/map_data.js   | 23 +++++++++++++----------
 code/utils_misc.js | 22 +++++++++++++++++++++-
 2 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/code/map_data.js b/code/map_data.js
index e52a0fc0..37729ed1 100644
--- a/code/map_data.js
+++ b/code/map_data.js
@@ -14,10 +14,13 @@ window.requestData = function() {
 
   var bounds = clampLatLngBounds(map.getBounds());
 
-  var x1 = lngToTile(bounds.getWest(), map.getZoom());
-  var x2 = lngToTile(bounds.getEast(), map.getZoom());
-  var y1 = latToTile(bounds.getNorth(), map.getZoom());
-  var y2 = latToTile(bounds.getSouth(), map.getZoom());
+  //we query the server as if the zoom level was effectiveZoom
+  var z = getPortalDataZoom();
+
+  var x1 = lngToTile(bounds.getWest(), z);
+  var x2 = lngToTile(bounds.getEast(), z);
+  var y1 = latToTile(bounds.getNorth(), z);
+  var y2 = latToTile(bounds.getSouth(), z);
 
   // will group requests by second-last quad-key quadrant
   tiles = {};
@@ -25,16 +28,16 @@ window.requestData = function() {
   // walk in x-direction, starts right goes left
   for (var x = x1; x <= x2; x++) {
     for (var y = y1; y <= y2; y++) {
-      var tile_id = pointToTileId(map.getZoom(), x, y);
+      var tile_id = pointToTileId(z, x, y);
       var bucket = Math.floor(x / 2) + "" + Math.floor(y / 2);
       if (!tiles[bucket])
         tiles[bucket] = [];
       tiles[bucket].push(generateBoundsParams(
         tile_id,
-        tileToLat(y + 1, map.getZoom()),
-        tileToLng(x, map.getZoom()),
-        tileToLat(y, map.getZoom()),
-        tileToLng(x + 1, map.getZoom())
+        tileToLat(y + 1, z),
+        tileToLng(x, z),
+        tileToLat(y, z),
+        tileToLng(x + 1, z)
       ));
     }
   }
@@ -43,7 +46,7 @@ window.requestData = function() {
   portalRenderLimit.init();
   // finally send ajax requests
   $.each(tiles, function(ind, tls) {
-    data = { zoom: map.getZoom() };
+    data = { zoom: z };
     data.boundsParamsList = tls;
     window.requests.add(window.postAjax('getThinnedEntitiesV2', data, window.handleDataResponse, window.handleFailedRequest));
   });
diff --git a/code/utils_misc.js b/code/utils_misc.js
index 2e7f3578..2d2cccc4 100644
--- a/code/utils_misc.js
+++ b/code/utils_misc.js
@@ -228,8 +228,28 @@ window.renderLimitReached = function(ratio) {
   return param.reached;
 }
 
-window.getMinPortalLevel = function() {
+window.getPortalDataZoom = function() {
   var z = map.getZoom();
+
+  // limiting the mazimum zoom level for data retrieval reduces the number of requests at high zoom levels
+  // (as all portal data is retrieved at z=17, why retrieve multiple z=18 tiles when fewer z=17 would do?)
+  // a potential downside - we end up requesting more data than we needed from the larger tiles that go off
+  // the window edge. 
+  if (z > 17) z=17;
+
+  // we could consider similar zoom-level consolidation, as, e.g. level 16 and 15 both return L1+, always
+  // request zoom 15 tiles. however, there are quirks in the current data stream, where small fields aren't
+  // returned by the server. using larger tiles always would amplify this issue.
+
+
+  //sanity check - should never happen
+  if (z < 0) z=0;
+
+  return z;
+}
+
+window.getMinPortalLevel = function() {
+  var z = getPortalDataZoom();
   if(z >= 17) return 0;
   if(z < 0) return 8;
   var conv = [8,8,8,8,7,7,6,6,5,4,4,3,3,2,2,1,1];