Move ol.Sphere#circle to ol.geom.Polygon.circular

Previously, ol.geom.Polygon was a transitive dependency of ol.proj (since ol.proj requires ol.sphere.NORMAL, and all spheres were capable of generating circular polygons).  Instead, ol.proj should be lower-level.  Since it deals only with coordinate arrays, it shouldn't depend on all of the geometry code.

By adding a static `circular` function to `ol.geom.Polygon`, the dependency tree makes more sense.  If you want to create a polygon that approximates a circle on a sphere, you require `ol.geom.Polygon` and `ol.Sphere` (or one of the constants).

This makes room for geometries to have a `transform` method that takes projection-like arguments (meaning that `ol.geom.Geometry` will require `ol.proj`).

examples/tissot.js

@@ -1,6 +1,7 @@
 goog.require('ol.Feature');
 goog.require('ol.Map');
 goog.require('ol.View2D');
+goog.require('ol.geom.Polygon');
 goog.require('ol.layer.Tile');
 goog.require('ol.layer.Vector');
 goog.require('ol.source.TileWMS');
@@ -38,7 +39,7 @@ var map = new ol.Map({
 var radius = 800000;
 for (var x = -180; x < 180; x += 30) {
   for (var y = -90; y < 90; y += 30) {
-    var geometry = ol.sphere.WGS84.circle([x, y], radius, 64);
-    vectorSource.addFeature(new ol.Feature(geometry));
+    var circle = ol.geom.Polygon.circular(ol.sphere.WGS84, [x, y], radius, 64);
+    vectorSource.addFeature(new ol.Feature(circle));
   }
 }

src/ol/geolocation.js

@@ -11,6 +11,7 @@ goog.require('ol.BrowserFeature');
 goog.require('ol.Coordinate');
 goog.require('ol.Object');
 goog.require('ol.geom.Geometry');
+goog.require('ol.geom.Polygon');
 goog.require('ol.proj');
 goog.require('ol.sphere.WGS84');
 
@@ -186,7 +187,8 @@ ol.Geolocation.prototype.positionChange_ = function(position) {
   this.set(ol.GeolocationProperty.POSITION, projectedPosition);
   this.set(ol.GeolocationProperty.SPEED,
       goog.isNull(coords.speed) ? undefined : coords.speed);
-  var geometry = ol.sphere.WGS84.circle(this.position_, coords.accuracy);
+  var geometry = ol.geom.Polygon.circular(
+      ol.sphere.WGS84, this.position_, coords.accuracy);
   geometry.applyTransform(this.transform_);
   this.set(ol.GeolocationProperty.ACCURACY_GEOMETRY, geometry);
   this.dispatchChangeEvent();

src/ol/geom/polygon.js

@@ -314,3 +314,29 @@ ol.geom.Polygon.prototype.setFlatCoordinates =
   this.ends_ = ends;
   this.dispatchChangeEvent();
 };
+
+
+/**
+ * Create an approximation of a circle on the surface of a sphere.
+ * @param {ol.Sphere} sphere The sphere.
+ * @param {ol.Coordinate} center Center.
+ * @param {number} radius Radius.
+ * @param {number=} opt_n Optional number of points.  Default is `32`.
+ * @return {ol.geom.Polygon} Circle geometry.
+ * @todo api
+ */
+ol.geom.Polygon.circular = function(sphere, center, radius, opt_n) {
+  var n = goog.isDef(opt_n) ? opt_n : 32;
+  /** @type {Array.<number>} */
+  var flatCoordinates = [];
+  var i;
+  for (i = 0; i < n; ++i) {
+    goog.array.extend(
+        flatCoordinates, sphere.offset(center, radius, 2 * Math.PI * i / n));
+  }
+  flatCoordinates.push(flatCoordinates[0], flatCoordinates[1]);
+  var polygon = new ol.geom.Polygon(null);
+  polygon.setFlatCoordinates(
+      ol.geom.GeometryLayout.XY, flatCoordinates, [flatCoordinates.length]);
+  return polygon;
+};

src/ol/sphere/sphere.js

@@ -12,7 +12,6 @@ goog.provide('ol.Sphere');
 
 goog.require('goog.array');
 goog.require('goog.math');
-goog.require('ol.geom.Polygon');
 
 
 
@@ -30,33 +29,6 @@ ol.Sphere = function(radius) {
 };
 
 
-/**
- * Returns an approximation to a circle centered on `center` with radius
- * `radius` with `n` distinct points.
- *
- * @param {ol.Coordinate} center Center.
- * @param {number} radius Radius.
- * @param {number=} opt_n N.
- * @return {ol.geom.Geometry} Circle geometry.
- * @todo api
- */
-ol.Sphere.prototype.circle = function(center, radius, opt_n) {
-  var n = goog.isDef(opt_n) ? opt_n : 32;
-  /** @type {Array.<number>} */
-  var flatCoordinates = [];
-  var i;
-  for (i = 0; i < n; ++i) {
-    goog.array.extend(
-        flatCoordinates, this.offset(center, radius, 2 * Math.PI * i / n));
-  }
-  flatCoordinates.push(flatCoordinates[0], flatCoordinates[1]);
-  var polygon = new ol.geom.Polygon(null);
-  polygon.setFlatCoordinates(
-      ol.geom.GeometryLayout.XY, flatCoordinates, [flatCoordinates.length]);
-  return polygon;
-};
-
-
 /**
  * Returns the distance from c1 to c2 using the spherical law of cosines.
  *