Improve docs for getPointResolution functions

externs/olx.js

@@ -680,7 +680,8 @@ olx.ProjectionOptions.prototype.worldExtent;
 /**
  * Function to determine resolution at a point. The function is called with a
  * `{number}` view resolution and an `{ol.Coordinate}` as arguments, and returns
- * the `{number}` resolution at the passed coordinate.
+ * the `{number}` resolution at the passed coordinate. If this is `undefined`,
+ * the default {@link ol.proj#getPointResolution} function will be used.
  * @type {(function(number, ol.Coordinate):number|undefined)}
  * @api
  */

src/ol/proj.js

@@ -44,9 +44,14 @@ if (ol.ENABLE_PROJ4JS) {
  * Get the resolution of the point in degrees or distance units.
  * For projections with degrees as the unit this will simply return the
  * provided resolution. For other projections the point resolution is
- * estimated by transforming the 'point' pixel to EPSG:4326,
+ * by default estimated by transforming the 'point' pixel to EPSG:4326,
  * measuring its width and height on the normal sphere,
  * and taking the average of the width and height.
+ * A custom function can be provided for a specific projection, either
+ * by setting the `getPointResolution` option in the
+ * {@link ol.proj.Projection} constructor or by using
+ * {@link ol.proj.Projection#setGetPointResolution} to change an existing
+ * projection object.
  * @param {ol.proj.Projection} projection The projection.
  * @param {number} resolution Nominal resolution in projection units.
  * @param {ol.Coordinate} point Point to find adjusted resolution at.

src/ol/proj/projection.js

@@ -254,7 +254,8 @@ ol.proj.Projection.prototype.setWorldExtent = function(worldExtent) {
 
 
 /**
- * Set the getPointResolution function for this projection.
+ * Set the getPointResolution function (see {@link ol.proj#getPointResolution}
+ * for this projection.
  * @param {function(number, ol.Coordinate):number} func Function
  * @api
  */