feature(Extent): add methods to calculate extent dimensions.

* planarDimensions
* geodesicDimensions
* earthEuclideanDimensions

src/Core/Geographic/Extent.js

@@ -16,7 +16,9 @@ const dimensionTile = new THREE.Vector2();
 const defaultScheme = new THREE.Vector2(2, 2);
 const r = { row: 0, col: 0, invDiff: 0 };
 
-const coord =  new Coordinates('EPSG:4326', 0, 0, 0);
+const cNorthWest =  new Coordinates('EPSG:4326', 0, 0, 0);
+const cSouthWest =  new Coordinates('EPSG:4326', 0, 0, 0);
+const cNorthEast =  new Coordinates('EPSG:4326', 0, 0, 0);
 
 const southWest = new THREE.Vector3();
 const northEast = new THREE.Vector3();
@@ -256,11 +258,67 @@ class Extent {
     * @return {THREE.Vector2}
     */
     dimensions(target = new THREE.Vector2()) {
+        console.warn('Extent.dimensions is deprecated, use planarDimensions, geodesicDimensions or geodesicChordDimensions');
         target.x = Math.abs(this.east - this.west);
         target.y = Math.abs(this.north - this.south);
         return target;
     }
 
+    /**
+     *  Planar dimensions are two planar distances west/east and south/north.
+     *  Planar distance straight-line Euclidean distance calculated in a 2D Cartesian coordinate system.
+     *
+     * @param      {THREE.Vector2}  [target=new THREE.Vector2()]  The target
+     * @return     {THREE.Vector2}  Planar dimensions
+     */
+    planarDimensions(target = new THREE.Vector2()) {
+        // Calculte the dimensions for x and y
+        return target.set(Math.abs(this.east - this.west), Math.abs(this.north - this.south));
+    }
+
+    /**
+     *  Geodesic dimensions are two planar distances west/east and south/north.
+     *  Geodesic distance is calculated in an ellispoid space as the distance
+     *  across the curved surface of the world.
+     *
+     * @param      {THREE.Vector2}  [target=new THREE.Vector2()]  The target
+     * @return     {THREE.Vector2}  Planar dimensions
+     */
+    geodesicDimensions(target = new THREE.Vector2()) {
+        // set 3 corners extent
+        cNorthWest.crs = this.crs;
+        cSouthWest.crs = this.crs;
+        cNorthEast.crs = this.crs;
+
+        cNorthWest.setFromValues(this.west, this.north, 0);
+        cSouthWest.setFromValues(this.west, this.south, 0);
+        cNorthEast.setFromValues(this.east, this.north, 0);
+
+        // calcul geodesic distance northWest/northEast and northWest/southWest
+        return target.set(cNorthWest.geodesicDistanceTo(cNorthEast), cNorthWest.geodesicDistanceTo(cSouthWest));
+    }
+
+    /**
+     *  Earth euclidean dimensions are two earth euclidean distances between west/east and south/north.
+     *  Earth euclidean distance chord is calculated in a ellispoid space.
+     *
+     * @param      {THREE.Vector2}  [target=new THREE.Vector2()]  The target
+     * @return     {THREE.Vector2}  Earth euclidean dimensions
+     */
+    earthEuclideanDimensions(target = new THREE.Vector2()) {
+        // set 3 corners extent
+        cNorthWest.crs = this.crs;
+        cSouthWest.crs = this.crs;
+        cNorthEast.crs = this.crs;
+
+        cNorthWest.setFromValues(this.west, this.north, 0);
+        cSouthWest.setFromValues(this.west, this.south, 0);
+        cNorthEast.setFromValues(this.east, this.north, 0);
+
+        // calcul chord distance northWest/northEast and northWest/southWest
+        return target.set(cNorthWest.earthEuclideanDistanceTo(cNorthEast), cNorthWest.earthEuclideanDistanceTo(cSouthWest));
+    }
+
     /**
      * Return true if `coord` is inside the bounding box.
      *
@@ -546,10 +604,11 @@ class Extent {
             // if geocentric reproject box on 'EPSG:4326'
             crs = 'EPSG:4326';
             box = _box.copy(box);
-            coord.crs = crs;
-            coord.setFromVector3(box.min).as(crs, coord).toVector3(box.min);
-            coord.crs = crs;
-            coord.setFromVector3(box.max).as(crs, coord).toVector3(box.max);
+
+            cSouthWest.crs = crs;
+            cSouthWest.setFromVector3(box.min).as(crs, cSouthWest).toVector3(box.min);
+            cNorthEast.crs = crs;
+            cNorthEast.setFromVector3(box.max).as(crs, cNorthEast).toVector3(box.max);
         }
 
         return new Extent(crs, {

test/unit/extent.js

@@ -1,8 +1,11 @@
 import assert from 'assert';
-import { Box3, Vector3, Matrix4, Quaternion } from 'three';
+import { Box3, Vector3, Vector2, Matrix4, Quaternion } from 'three';
 import Coordinates from 'Core/Geographic/Coordinates';
 import Extent from 'Core/Geographic/Extent';
 import CRS from 'Core/Geographic/Crs';
+import proj4 from 'proj4';
+
+proj4.defs('EPSG:2154', '+proj=lcc +lat_1=49 +lat_2=44 +lat_0=46.5 +lon_0=3 +x_0=700000 +y_0=6600000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs');
 
 describe('Extent', function () {
     const minX = 0;
@@ -95,16 +98,42 @@ describe('Extent', function () {
         assert.strictEqual(subdivided[3].north, 0);
     });
 
-    it('should return the correct dimension of the extent', function () {
+    it('should return the correct planar dimensions', function () {
         const extent = new Extent('EPSG:4326', -15, 10, -10, 10);
-        const dimensions = extent.dimensions();
+        const dimensions = extent.planarDimensions();
 
         // Width
         assert.equal(dimensions.x, 25);
         // Height
         assert.equal(dimensions.y, 20);
     });
 
+    it('should return the same planar dimensions with deprecated dimensions method', function () {
+        const extent = new Extent('EPSG:4326', -15, 10, -10, 10);
+        const dimensions = extent.planarDimensions();
+        const dimensions_2 = extent.dimensions();
+        assert.equal(dimensions.x, dimensions_2.x);
+        assert.equal(dimensions.y, dimensions_2.y);
+    });
+
+    it('should return the correct earth euclidean dimensions', function () {
+        const extent = new Extent('EPSG:4326', 3, 3.01, 46, 46.01);
+        const dimensions = new Vector2();
+
+        extent.earthEuclideanDimensions(dimensions);
+        assert.equal(dimensions.x, 774.4934293643765);
+        assert.equal(dimensions.y, 1111.5141604285038);
+    });
+
+    it('should return the correct geodesic dimensions', function () {
+        const extent = new Extent('EPSG:4326', 3, 3.01, 46, 46.01);
+        const dimensions = new Vector2();
+
+        extent.geodesicDimensions(dimensions);
+        assert.equal(dimensions.x, 773.2375602074535);
+        assert.equal(dimensions.y, 1113.3197697640906);
+    });
+
     it('should clone extent like expected', function () {
         const withValues = new Extent('EPSG:4326', [minX, maxX, minY, maxY]);
         const clonedExtent = withValues.clone();
@@ -168,7 +197,7 @@ describe('Extent', function () {
     });
     it('should return dimensions of extent expected', function () {
         const withValues = new Extent('EPSG:4326', [minX, maxX, minY, maxY]);
-        const dimensions = withValues.dimensions();
+        const dimensions = withValues.planarDimensions();
         assert.equal(10, dimensions.x);
         assert.equal(4, dimensions.y);
     });