Function for creating tile grids from extents

src/ol/tilegrid/tilegrid.js

@@ -8,6 +8,7 @@ goog.require('ol.TileCoord');
 goog.require('ol.TileRange');
 goog.require('ol.array');
 goog.require('ol.extent');
+goog.require('ol.extent.Corner');
 goog.require('ol.proj.METERS_PER_UNIT');
 goog.require('ol.proj.Projection');
 goog.require('ol.proj.Units');
@@ -404,31 +405,62 @@ ol.tilegrid.getForProjection = function(projection) {
 
 
 /**
- * @param {ol.proj.Projection} projection Projection.
+ * @param {ol.Extent} extent Extent.
- * @param {number=} opt_maxZoom Maximum zoom level.
+ * @param {number=} opt_maxZoom Maximum zoom level (default is
- * @param {number=} opt_tileSize Tile size.
+ *     ol.DEFAULT_MAX_ZOOM).
+ * @param {number=} opt_tileSize Tile size (default uses ol.DEFAULT_TILE_SIZE).
+ * @param {ol.extent.Corner=} opt_corner Extent corner (default is
+ *     ol.extent.Corner.BOTTOM_LEFT).
  * @return {ol.tilegrid.TileGrid} TileGrid instance.
  */
-ol.tilegrid.createForProjection =
+ol.tilegrid.createForExtent =
-    function(projection, opt_maxZoom, opt_tileSize) {
+    function(extent, opt_maxZoom, opt_tileSize, opt_corner) {
-  var projectionExtent = projection.getExtent();
-  var size = goog.isNull(projectionExtent) ?
-      360 * ol.proj.METERS_PER_UNIT[ol.proj.Units.DEGREES] /
-          projection.getMetersPerUnit() :
-      Math.max(projectionExtent[2] - projectionExtent[0],
-          projectionExtent[3] - projectionExtent[1]);
   var maxZoom = goog.isDef(opt_maxZoom) ?
       opt_maxZoom : ol.DEFAULT_MAX_ZOOM;
-  var tileSize = goog.isDef(opt_tileSize) ? opt_tileSize : ol.DEFAULT_TILE_SIZE;
+
+  var tileSize = goog.isDef(opt_tileSize) ?
+      opt_tileSize : ol.DEFAULT_TILE_SIZE;
+
+  var corner = goog.isDef(opt_corner) ?
+      opt_corner : ol.extent.Corner.BOTTOM_LEFT;
+
+  var extentHeight = ol.extent.getHeight(extent);
+  var extentWidth = ol.extent.getWidth(extent);
+
+  var maxResolution = Math.max(
+      extentWidth / tileSize, extentHeight / tileSize);
+
   var resolutions = new Array(maxZoom + 1);
-  var maxResolution = size / tileSize;
+
   for (var z = 0, zz = resolutions.length; z < zz; ++z) {
     resolutions[z] = maxResolution / Math.pow(2, z);
   }
+
   return new ol.tilegrid.TileGrid({
-    origin: goog.isNull(projectionExtent) ? [0, 0] :
+    origin: ol.extent.getCorner(extent, corner),
-        ol.extent.getBottomLeft(projectionExtent),
     resolutions: resolutions,
     tileSize: tileSize
   });
 };
+
+
+/**
+ * @param {ol.proj.Projection} projection Projection.
+ * @param {number=} opt_maxZoom Maximum zoom level (default is
+ *     ol.DEFAULT_MAX_ZOOM).
+ * @param {number=} opt_tileSize Tile size (default uses ol.DEFAULT_TILE_SIZE).
+ * @param {ol.extent.Corner=} opt_corner Extent corner (default is
+ *     ol.extent.Corner.BOTTOM_LEFT).
+ * @return {ol.tilegrid.TileGrid} TileGrid instance.
+ */
+ol.tilegrid.createForProjection =
+    function(projection, opt_maxZoom, opt_tileSize, opt_corner) {
+  var extent = projection.getExtent();
+  if (goog.isNull(extent)) {
+    var half = 180 * ol.proj.METERS_PER_UNIT[ol.proj.Units.DEGREES] /
+        projection.getMetersPerUnit();
+    extent = ol.extent.createOrUpdate(-half, -half, half, half);
+  }
+  return ol.tilegrid.createForExtent(
+      extent, opt_maxZoom, opt_tileSize, opt_corner);
+};

test/spec/ol/tilegrid/tilegrid.test.js

@@ -161,6 +161,18 @@ describe('ol.tilegrid.TileGrid', function() {
     });
   });
 
+  describe('createForExtent', function() {
+    it('allows creation of tile grid from extent', function() {
+      var extent = ol.extent.createOrUpdate(-100, -100, 100, 100);
+      var grid = ol.tilegrid.createForExtent(extent);
+      expect(grid).to.be.a(ol.tilegrid.TileGrid);
+
+      var resolutions = grid.getResolutions();
+      expect(resolutions.length).to.be(ol.DEFAULT_MAX_ZOOM + 1);
+      expect(grid.getOrigin()).to.eql([-100, -100]);
+    });
+  });
+
   describe('createForProjection', function() {
 
     it('allows easier creation of a tile grid', function() {
@@ -200,6 +212,50 @@ describe('ol.tilegrid.TileGrid', function() {
           ol.DEFAULT_TILE_SIZE / Math.pow(2, 5));
     });
 
+    it('assumes origin is bottom-left', function() {
+      var projection = ol.proj.get('EPSG:3857');
+      var grid = ol.tilegrid.createForProjection(projection);
+      var origin = grid.getOrigin();
+      var half = ol.proj.EPSG3857.HALF_SIZE;
+      expect(origin).to.eql([-half, -half]);
+    });
+
+    it('accepts bottom-left as corner', function() {
+      var projection = ol.proj.get('EPSG:3857');
+      var grid = ol.tilegrid.createForProjection(
+          projection, undefined, undefined, ol.extent.Corner.BOTTOM_LEFT);
+      var origin = grid.getOrigin();
+      var half = ol.proj.EPSG3857.HALF_SIZE;
+      expect(origin).to.eql([-half, -half]);
+    });
+
+    it('accepts bottom-right as corner', function() {
+      var projection = ol.proj.get('EPSG:3857');
+      var grid = ol.tilegrid.createForProjection(
+          projection, undefined, undefined, ol.extent.Corner.BOTTOM_RIGHT);
+      var origin = grid.getOrigin();
+      var half = ol.proj.EPSG3857.HALF_SIZE;
+      expect(origin).to.eql([half, -half]);
+    });
+
+    it('accepts top-left as corner', function() {
+      var projection = ol.proj.get('EPSG:3857');
+      var grid = ol.tilegrid.createForProjection(
+          projection, undefined, undefined, ol.extent.Corner.TOP_LEFT);
+      var origin = grid.getOrigin();
+      var half = ol.proj.EPSG3857.HALF_SIZE;
+      expect(origin).to.eql([-half, half]);
+    });
+
+    it('accepts top-right as corner', function() {
+      var projection = ol.proj.get('EPSG:3857');
+      var grid = ol.tilegrid.createForProjection(
+          projection, undefined, undefined, ol.extent.Corner.TOP_RIGHT);
+      var origin = grid.getOrigin();
+      var half = ol.proj.EPSG3857.HALF_SIZE;
+      expect(origin).to.eql([half, half]);
+    });
+
   });
 
   describe('getForProjection', function() {
@@ -643,8 +699,12 @@ describe('ol.tilegrid.TileGrid', function() {
 });
 
 goog.require('ol.Coordinate');
+goog.require('ol.extent');
+goog.require('ol.extent.Corner');
 goog.require('ol.proj');
 goog.require('ol.proj.METERS_PER_UNIT');
+goog.require('ol.proj');
+goog.require('ol.proj.EPSG3857');
 goog.require('ol.proj.Projection');
 goog.require('ol.proj.Units');
 goog.require('ol.tilegrid.TileGrid');