Merge pull request #2349 from probins/projdocs

Improve docs for projection

src/ol/proj/proj.js

@@ -52,16 +52,14 @@ ol.proj.METERS_PER_UNIT[ol.proj.Units.METERS] = 1;
 
 /**
  * @classdesc
- * Class for coordinate transforms between coordinate systems. By default,
- * OpenLayers ships with the ability to transform coordinates between
- * geographic (EPSG:4326) and web or spherical mercator (EPSG:3857)
- * coordinate reference systems. Any transform functions can be added with
- * {@link ol.proj.addCoordinateTransforms}.
+ * Projection definition class. One of these is created for each projection
+ * supported in the application and stored in the {@link ol.proj} namespace.
+ * You can use these in applications, but this is not required, as API params
+ * and options use {@link ol.proj.ProjectionLike} which means the simple string
+ * code will suffice.
  *
- * Additional transforms may be added by using the {@link http://proj4js.org/}
- * library. If the proj4js library is loaded, transforms will work between any
- * coordinate reference systems with proj4js definitions. These definitions can
- * be obtained from {@link http://epsg.io/}.
+ * You can use {@link ol.proj.get} to retrieve the object for a particular
+ * projection.
  *
  * @constructor
  * @param {olx.ProjectionOptions} options Projection options.
@@ -369,6 +367,9 @@ ol.proj.addTransform = function(source, destination, transformFn) {
 /**
  * Registers coordinate transform functions to convert coordinates between the
  * source projection and the destination projection.
+ * The forward and inverse functions convert coordinate pairs; this function
+ * converts these into the functions used internally which also handle
+ * extents and coordinate arrays.
  *
  * @param {ol.proj.ProjectionLike} source Source projection.
  * @param {ol.proj.ProjectionLike} destination Destination projection.