Add MapUtils.getResolutionsForScales() for arbitrary projections

geosolutions-it · Dec 7, 2016 · 072c32b · 072c32b
1 parent 37d6142
commit 072c32b
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Showing 2 changed files with 71 additions and 10 deletions.
diff --git a/web/client/utils/MapUtils.js b/web/client/utils/MapUtils.js
@@ -8,6 +8,13 @@
 
 const DEFAULT_SCREEN_DPI = 96;
 
+const METERS_PER_UNIT = {
+    'm': 1,
+    'degrees': 111194.87428468118,
+    'ft': 0.3048,
+    'us-ft': 1200 / 3937
+};
+
 const GOOGLE_MERCATOR = {
     RADIUS: 6378137,
     TILE_WIDTH: 256,
@@ -51,6 +58,16 @@ function dpi2dpm(dpi) {
     return dpi * (100 / 2.54);
 }
 
+/**
+ * @param dpi {number} screen resolution in dots per inch.
+ * @param projection {string} map projection.
+ * @return {number} dots per map unit.
+ */
+function dpi2dpu(dpi, projection) {
+    const units = CoordinatesUtils.getUnits(projection || "EPSG:3857");
+    return METERS_PER_UNIT[units] * dpi2dpm(dpi || DEFAULT_SCREEN_DPI);
+}
+
 /**
  * @param radius {number} Earth's radius of the model in meters.
  * @param tileWidth {number} width of the tiles used to draw the map.
@@ -114,14 +131,22 @@ function getGoogleMercatorScales(minZoom, maxZoom, dpi) {
     );
 }
 
-function getResolutionsFromScales(scales, dpi) {
-    const dpm = dpi2dpm((dpi || DEFAULT_SCREEN_DPI));
-
-    return scales.map((scale) => scale / dpm);
+/**
+ * @param scales {array} list of scales.
+ * @param projection {string} map projection.
+ * @param dpi {number} screen resolution in dots per inch.
+ * @return {array} a list of resolutions corresponding to the given scales, projection and dpi.
+ */
+function getResolutionsForScales(scales, projection, dpi) {
+    const dpu = dpi2dpu(dpi, projection);
+    const resolutions = scales.map((scale) => {
+        return scale / dpu;
+    });
+    return resolutions;
 }
 
 function getGoogleMercatorResolutions(minZoom, maxZoom, dpi) {
-    return getResolutionsFromScales(getGoogleMercatorScales(minZoom, maxZoom, dpi), dpi);
+    return getResolutionsForScales(getGoogleMercatorScales(minZoom, maxZoom, dpi), "EPSG:3857", dpi);
 }
 
 function getResolutions() {
@@ -132,9 +157,8 @@ function getResolutions() {
 }
 
 function getScales(projection, dpi) {
-    const units = CoordinatesUtils.getUnits(projection);
-    const dpm = dpi2dpm((dpi || DEFAULT_SCREEN_DPI));
-    return getResolutions().map((resolution) => resolution * dpm * (units === 'degrees' ? 111194.87428468118 : 1));
+    const dpu = dpi2dpu(dpi, projection);
+    return getResolutions().map((resolution) => resolution * dpu);
 }
 
 function defaultGetZoomForExtent(extent, mapSize, minZoom, maxZoom, dpi, mapResolutions) {
@@ -145,8 +169,8 @@ function defaultGetZoomForExtent(extent, mapSize, minZoom, maxZoom, dpi, mapReso
     const yResolution = Math.abs(hExtent / mapSize.height);
     const extentResolution = Math.max(xResolution, yResolution);
 
-    const resolutions = mapResolutions || getResolutionsFromScales(getGoogleMercatorScales(
-        minZoom, maxZoom, (dpi || DEFAULT_SCREEN_DPI)));
+    const resolutions = mapResolutions || getResolutionsForScales(getGoogleMercatorScales(
+        minZoom, maxZoom, (dpi || DEFAULT_SCREEN_DPI)), "EPSG:3857", dpi);
 
     const {zoom, ...other} = resolutions.reduce((previous, resolution, index) => {
         const diff = Math.abs(resolution - extentResolution);
@@ -258,6 +282,7 @@ module.exports = {
     getGoogleMercatorScales,
     getGoogleMercatorResolutions,
     getGoogleMercatorScale,
+    getResolutionsForScales,
     getZoomForExtent,
     defaultGetZoomForExtent,
     getCenterForExtent,

diff --git a/web/client/utils/__tests__/MapUtils-test.js b/web/client/utils/__tests__/MapUtils-test.js
@@ -19,6 +19,7 @@ var {
     getGoogleMercatorScales,
     getGoogleMercatorResolutions,
     getGoogleMercatorScale,
+    getResolutionsForScales,
     getZoomForExtent,
     getCenterForExtent,
     getBbox,
@@ -46,6 +47,41 @@ describe('Test the MapUtils', () => {
     it('getGoogleMercatorScales', () => {
         expect(getGoogleMercatorScales(1, 1, 1).length).toBe(1);
     });
+    it('getResolutionsForScales', () => {
+        // generate test scales for resolutions
+        function testScales(resolutions, dpu) {
+            return resolutions.map((res) => {
+                return res * dpu;
+            });
+        }
+
+        function dotsPerUnit(dpi, metersPerUnit) {
+            return metersPerUnit * dpi * 100 / 2.54;
+        }
+
+        function resolutionsEqual(arrayA, arrayB) {
+            if (arrayA.length === arrayB.length) {
+                for (let i in arrayA) {
+                    // check if absolute difference is within epsilon
+                    if (Math.abs(arrayA[i] - arrayB[i]) > 1E-6) {
+                        return false;
+                    }
+                }
+                return true;
+            }
+            return false;
+        }
+
+        const mPerDegree = 111194.87428468118;
+        let resolutions = [10000, 1000, 100, 10, 1];
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(96, 1)), "EPSG:3857", 96), resolutions)).toBe(true);
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(96, mPerDegree)), "EPSG:4326", 96), resolutions)).toBe(true);
+        resolutions = [32000, 16000, 8000, 4000, 2000, 1000, 500, 250];
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(96, 1)), "EPSG:3857", 96), resolutions)).toBe(true);
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(96, mPerDegree)), "EPSG:4326", 96), resolutions)).toBe(true);
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(120, 1)), "EPSG:3857", 120), resolutions)).toBe(true);
+        expect(resolutionsEqual(getResolutionsForScales(testScales(resolutions, dotsPerUnit(120, mPerDegree)), "EPSG:4326", 120), resolutions)).toBe(true);
+    });
     it('getZoomForExtent without hook', () => {
         var extent = [1880758.3574092742, 6084533.340409827, 1291887.4915002766, 5606954.787684047];
         var mapSize = {height: 781, width: 963};