Add decimals option to format write

externs/olx.js

@@ -1632,7 +1632,8 @@ olx.format.ReadOptions.prototype.featureProjection;
 /**
  * @typedef {{dataProjection: ol.proj.ProjectionLike,
  *     featureProjection: ol.proj.ProjectionLike,
- *     rightHanded: (boolean|undefined)}}
+ *     rightHanded: (boolean|undefined),
+ *     decimals: (number|undefined)}}
  * @api
  */
 olx.format.WriteOptions;
@@ -1675,6 +1676,20 @@ olx.format.WriteOptions.prototype.featureProjection;
 olx.format.WriteOptions.prototype.rightHanded;
 
 
+/**
+ * Maximum number of decimal places for coordinates. Coordinates are stored
+ * internally as floats, but floating-point arithmetic can create coordinates
+ * with a large number of decimal places, not generally wanted on output.
+ * Set a number here to round coordinates. Can also be used to ensure that
+ * coordinates read in can be written back out with the same number of decimals.
+ * Default is no rounding.
+ *
+ * @type {number|undefined}
+ * @api
+ */
+olx.format.WriteOptions.prototype.decimals;
+
+
 /**
  * @typedef {{defaultDataProjection: ol.proj.ProjectionLike,
  *     geometryName: (string|undefined)}}

src/ol/format/featureformat.js

@@ -71,6 +71,9 @@ ol.format.Feature.prototype.adaptOptions = function(options) {
           options.dataProjection : this.defaultDataProjection,
       rightHanded: options.rightHanded
     };
+    if (options.decimals) {
+      updatedOptions.decimals = options.decimals;
+    }
   }
   return updatedOptions;
 };
@@ -165,21 +168,45 @@ ol.format.Feature.transformWithOptions = function(
       ol.proj.get(opt_options.featureProjection) : null;
   var dataProjection = opt_options ?
       ol.proj.get(opt_options.dataProjection) : null;
+  /**
+   * @type {ol.geom.Geometry|ol.Extent}
+   */
+  var transformed;
   if (featureProjection && dataProjection &&
       !ol.proj.equivalent(featureProjection, dataProjection)) {
     if (geometry instanceof ol.geom.Geometry) {
-      return (write ? geometry.clone() : geometry).transform(
+      transformed = (write ? geometry.clone() : geometry).transform(
           write ? featureProjection : dataProjection,
           write ? dataProjection : featureProjection);
     } else {
       // FIXME this is necessary because ol.format.GML treats extents
       // as geometries
-      return ol.proj.transformExtent(
+      transformed = ol.proj.transformExtent(
           write ? geometry.slice() : geometry,
           write ? featureProjection : dataProjection,
           write ? dataProjection : featureProjection);
     }
   } else {
-    return geometry;
+    transformed = geometry;
   }
+  if (write && opt_options && opt_options.decimals) {
+    var power = Math.pow(10, opt_options.decimals);
+    // if decimals option on write, round each coordinate appropriately
+    /**
+     * @param {Array.<number>} coordinates Coordinates.
+     * @return {Array.<number>} Transformed coordinates.
+     */
+    var transform = function(coordinates) {
+      for (var i = 0, ii = coordinates.length; i < ii; ++i) {
+        coordinates[i] = Math.round(coordinates[i] * power) / power;
+      }
+      return coordinates;
+    };
+    if (Array.isArray(transformed)) {
+      transform(/** @type {ol.Extent} */ (transformed));
+    } else {
+      transformed.applyTransform(transform);
+    }
+  }
+  return transformed;
 };

test/spec/ol/format/geojsonformat.test.js

@@ -746,6 +746,26 @@ describe('ol.format.GeoJSON', function() {
       expect(geometries[1].getCoordinates()[0][1]).to.roughlyEqual(
           gotGeometries[1].getCoordinates()[0][1], 1e-8);
     });
+
+    it('truncates transformed point with decimals option', function() {
+      var point = new ol.geom.Point([2, 3]).transform('EPSG:4326','EPSG:3857');
+      var geojson = format.writeGeometry(point, {
+        featureProjection: 'EPSG:3857',
+        decimals: 2
+      });
+      expect(format.readGeometry(geojson).getCoordinates()).to.eql(
+          [2, 3]);
+    });
+
+    it('truncates a linestring with decimals option', function() {
+      var linestring = new ol.geom.LineString([[42.123456789, 38.987654321],
+          [43, 39]]);
+      var geojson = format.writeGeometry(linestring, {
+        decimals: 6
+      });
+      expect(format.readGeometry(geojson).getCoordinates()).to.eql(
+          [[42.123457, 38.987654], [43, 39]]);
+    });
   });
 
 });