From 7d67ec41eb57d6a69c738259b27a2aab205fb933 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ir=C3=A9n=C3=A9e=20Dubourg?= <idubourg@cirilgroup.com>
Date: Thu, 5 Dec 2024 16:31:01 +0100
Subject: [PATCH] feat(wms): use proj4 crs axis param

---
 src/Core/Geographic/Crs.ts | 19 +++++++++++++++++++
 src/Source/WMSSource.js    | 39 ++++++++++++++++++++++++++++++++------
 test/unit/crs.js           |  6 ++++++
 3 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/src/Core/Geographic/Crs.ts b/src/Core/Geographic/Crs.ts
index 9580dcfb77..46213ec261 100644
--- a/src/Core/Geographic/Crs.ts
+++ b/src/Core/Geographic/Crs.ts
@@ -4,6 +4,12 @@ import type { ProjectionDefinition } from 'proj4';
 
 proj4.defs('EPSG:4978', '+proj=geocent +datum=WGS84 +units=m +no_defs');
 
+// Redefining proj4 global projections to match epsg.org database axis order.
+// See https://github.com/iTowns/itowns/pull/2465#issuecomment-2517024859
+proj4.defs('EPSG:4326').axis = 'neu';
+proj4.defs('EPSG:4269').axis = 'neu';
+proj4.defs('WGS84').axis = 'neu';
+
 /**
  * A projection as a CRS identifier string. This identifier references a
  * projection definition previously defined with
@@ -139,6 +145,19 @@ export function reasonableEpsilon(crs: ProjectionLike) {
     }
 }
 
+/**
+ * Returns the axis parameter defined in proj4 for the provided crs.
+ * Might be undefined depending on crs definition.
+ *
+ * @param crs - The CRS to get axis from.
+ * @returns the matching proj4 axis string, 'enu' for instance (east, north, up)
+ */
+export function axisOrder(crs: ProjectionLike) {
+    mustBeString(crs);
+    const projection = proj4.defs(crs);
+    return !projection ? undefined : projection.axis;
+}
+
 /**
  * Defines a proj4 projection as a named alias.
  * This function is a specialized wrapper over the
diff --git a/src/Source/WMSSource.js b/src/Source/WMSSource.js
index 7434e0bba6..41dab478b1 100644
--- a/src/Source/WMSSource.js
+++ b/src/Source/WMSSource.js
@@ -1,9 +1,38 @@
 import Source from 'Source/Source';
 import URLBuilder from 'Provider/URLBuilder';
 import Extent from 'Core/Geographic/Extent';
+import * as CRS from 'Core/Geographic/Crs';
 
 const _extent = new Extent('EPSG:4326', [0, 0, 0, 0]);
 
+/**
+ * Proj provides an optional param to define axis order and orientation for a
+ * given projection. 'enu' for instance stands for east, north, up.
+ * Elevation is not needed here. The two first characters are sufficient to map
+ * proj axis to iTowns bbox order formalism.
+ * 'enu' corresponds to 'wsen' because bbox starts by lower value coordinates
+ * and preserves axis ordering, here long/lat.
+ */
+const projAxisToBboxMappings = {
+    en: 'wsen',
+    es: 'wnes',
+    wn: 'eswn',
+    ws: 'enws',
+    ne: 'swne',
+    se: 'nwse',
+    nw: 'senw',
+    sw: 'nesw',
+};
+
+/**
+ * Provides the bbox axis order matching provided proj4 axis
+ * @param {string} projAxis the CRS axis order as defined in proj4
+ * @returns {string} the corresponding bbox axis order to use for WMS 1.3.0
+ */
+function projAxisToWmsBbox(projAxis) {
+    return projAxis && projAxisToBboxMappings[projAxis.slice(0, 2)] || 'wsen';
+}
+
 /**
  * An object defining the source of images to get from a
  * [WMS](http://www.opengeospatial.org/standards/wms) server. It inherits
@@ -104,13 +133,11 @@ class WMSSource extends Source {
 
         if (source.axisOrder) {
             this.axisOrder = source.axisOrder;
-        } else if (this.crs == 'EPSG:4326') {
-            // 4326 (lat/long) axis order depends on the WMS version used
-            // EPSG 4326 x = lat, long = y
-            // version 1.X.X long/lat while version 1.3.0 mandates xy (so lat,long)
-            this.axisOrder = this.version === '1.3.0' ? 'swne' : 'wsen';
+        } else if (this.version === '1.3.0') { // If not set, axis order depends on WMS version
+            // Version 1.3.0 depends on CRS axis order as defined in epsg.org database
+            this.axisOrder = projAxisToWmsBbox(CRS.axisOrder(this.crs));
         } else {
-            // xy,xy order
+            // Versions 1.X.X mandate long/lat order, east-north orientation
             this.axisOrder = 'wsen';
         }
 
diff --git a/test/unit/crs.js b/test/unit/crs.js
index 4f9a1caff1..cf3e64b201 100644
--- a/test/unit/crs.js
+++ b/test/unit/crs.js
@@ -53,4 +53,10 @@ describe('CRS assertions', function () {
         assert.strictEqual(CRS.reasonableEpsilon('EPSG:4326'), 0.01);
         assert.strictEqual(CRS.reasonableEpsilon('EPSG:3857'), 0.001);
     });
+
+    it('should return neu axis order', function () {
+        assert.equal(CRS.axisOrder('WGS84'), 'neu');
+        assert.equal(CRS.axisOrder('WGS84'), 'neu');
+        assert.equal(CRS.axisOrder('EPSG:4269'), 'neu');
+    });
 });