Adjust resolution for user extent

src/ol/proj.js

@@ -631,6 +631,44 @@ export function fromUserExtent(extent, destProjection) {
   return transformExtent(extent, userProjection, destProjection);
 }
 
+/**
+ * Return the resolution in user projection units per pixel. If no user projection
+ * is set, or source or user projection are missing units, the original resolution
+ * is returned.
+ * @param {number} resolution Resolution in input projection units per pixel.
+ * @param {ProjectionLike} sourceProjection The input projection.
+ * @return {number} Resolution in user projection units per pixel.
+ */
+export function toUserResolution(resolution, sourceProjection) {
+  if (!userProjection) {
+    return resolution;
+  }
+  const sourceUnits = get(sourceProjection).getUnits();
+  const userUnits = userProjection.getUnits();
+  return sourceUnits && userUnits
+    ? (resolution * METERS_PER_UNIT[sourceUnits]) / METERS_PER_UNIT[userUnits]
+    : resolution;
+}
+
+/**
+ * Return the resolution in user projection units per pixel. If no user projection
+ * is set, or source or user projection are missing units, the original resolution
+ * is returned.
+ * @param {number} resolution Resolution in user projection units per pixel.
+ * @param {ProjectionLike} destProjection The destination projection.
+ * @return {number} Resolution in destination projection units per pixel.
+ */
+export function fromUserResolution(resolution, destProjection) {
+  if (!userProjection) {
+    return resolution;
+  }
+  const sourceUnits = get(destProjection).getUnits();
+  const userUnits = userProjection.getUnits();
+  return sourceUnits && userUnits
+    ? (resolution * METERS_PER_UNIT[userUnits]) / METERS_PER_UNIT[sourceUnits]
+    : resolution;
+}
+
 /**
  * Creates a safe coordinate transform function from a coordinate transform function.
  * "Safe" means that it can handle wrapping of x-coordinates for global projections,

src/ol/renderer/canvas/VectorLayer.js

@@ -36,6 +36,7 @@ import {
   getTransformFromProjections,
   getUserProjection,
   toUserExtent,
+  toUserResolution,
 } from '../../proj.js';
 import {getUid} from '../../util.js';
 import {wrapX as wrapCoordinateX} from '../../coordinate.js';
@@ -642,9 +643,11 @@ class CanvasVectorLayerRenderer extends CanvasLayerRenderer {
     let userTransform;
     if (userProjection) {
       for (let i = 0, ii = loadExtents.length; i < ii; ++i) {
+        const extent = loadExtents[i];
+        const userExtent = toUserExtent(extent, projection);
         vectorSource.loadFeatures(
-          toUserExtent(loadExtents[i], projection),
-          resolution,
+          userExtent,
+          toUserResolution(resolution, projection),
           userProjection
         );
       }

src/ol/source/Vector.js

@@ -26,7 +26,7 @@ import {xhr} from '../featureloader.js';
  * returns an array of {@link module:ol/extent~Extent} with the extents to load. Usually this
  * is one of the standard {@link module:ol/loadingstrategy} strategies.
  *
- * @typedef {function(import("../extent.js").Extent, number): Array<import("../extent.js").Extent>} LoadingStrategy
+ * @typedef {function(import("../extent.js").Extent, number, import("../proj/Projection.js").default): Array<import("../extent.js").Extent>} LoadingStrategy
  * @api
  */
 
@@ -939,7 +939,7 @@ class VectorSource extends Source {
    */
   loadFeatures(extent, resolution, projection) {
     const loadedExtentsRtree = this.loadedExtentsRtree_;
-    const extentsToLoad = this.strategy_(extent, resolution);
+    const extentsToLoad = this.strategy_(extent, resolution, projection);
     for (let i = 0, ii = extentsToLoad.length; i < ii; ++i) {
       const extentToLoad = extentsToLoad[i];
       const alreadyLoaded = loadedExtentsRtree.forEachInExtent(

test/node/ol/proj.test.js

@@ -12,6 +12,7 @@ import {
   fromLonLat,
   fromUserCoordinate,
   fromUserExtent,
+  fromUserResolution,
   getPointResolution,
   get as getProjection,
   getTransform,
@@ -21,6 +22,7 @@ import {
   toLonLat,
   toUserCoordinate,
   toUserExtent,
+  toUserResolution,
   transform,
   transformExtent,
   useGeographic,
@@ -151,6 +153,36 @@ describe('ol/proj.js', function () {
     });
   });
 
+  describe('fromUserResolution()', function () {
+    it("adjusts a resolution for the user projection's units", function () {
+      useGeographic();
+      const user = 1 / METERS_PER_UNIT['degrees'];
+      const resolution = fromUserResolution(user, 'EPSG:3857');
+      expect(resolution).to.roughlyEqual(1, 1e-9);
+    });
+
+    it('returns the original if no user projection is set', function () {
+      const user = METERS_PER_UNIT['meters'];
+      const resolution = fromUserResolution(user, 'EPSG:3857');
+      expect(resolution).to.eql(user);
+    });
+  });
+
+  describe('toUserResolution()', function () {
+    it("adjusts a resolution for the user projection's units", function () {
+      useGeographic();
+      const dest = 1;
+      const resolution = toUserResolution(dest, 'EPSG:3857');
+      expect(resolution).to.eql(1 / METERS_PER_UNIT['degrees']);
+    });
+
+    it('returns the original if no user projection is set', function () {
+      const dest = METERS_PER_UNIT['degrees'];
+      const resolution = toUserResolution(dest, 'EPSG:3857');
+      expect(resolution).to.eql(dest);
+    });
+  });
+
   describe('toLonLat()', function () {
     const cases = [
       {