change interface to XYZ

lib/mbtiles.js

@@ -268,7 +268,7 @@ MBTiles.prototype.insertGridTiles = function(map, callback) {
     stmt.finalize(callback);
 };
 
-// Select a tile from an mbtiles database.
+// Select a tile from an mbtiles database. Scheme is XYZ.
 //
 // - @param {Number} x tile x coordinate.
 // - @param {Number} y tile y coordinate.
@@ -277,6 +277,9 @@ MBTiles.prototype.insertGridTiles = function(map, callback) {
 MBTiles.prototype.getTile = function(z, x, y, callback) {
     if (typeof callback !== 'function') callback = noop;
 
+    // Flip Y coordinate because MBTiles files are TMS.
+    y = Math.pow(2, z) - 1 - y;
+
     var mbtiles = this;
     this.db.get('SELECT tile_data FROM tiles WHERE ' +
         'zoom_level = ? AND tile_column = ? AND tile_row = ?',
@@ -297,7 +300,7 @@ MBTiles.prototype.getTile = function(z, x, y, callback) {
         });
 };
 
-// Select a grid and its data from an mbtiles database.
+// Select a grid and its data from an mbtiles database. Scheme is XYZ.
 //
 // - @param {Number} x tile x coordinate
 // - @param {Number} y tile y coordinate
@@ -306,6 +309,9 @@ MBTiles.prototype.getTile = function(z, x, y, callback) {
 MBTiles.prototype.getGrid = function(z, x, y, callback) {
     if (typeof callback !== 'function') callback = noop;
 
+    // Flip Y coordinate because MBTiles files are TMS.
+    y = Math.pow(2, z) - 1 - y;
+
     var that = this;
     Step(
         function() {