Fixed ellipsoid being used instead of a sphere in EPSG:3857 (Web Merc…

…ator)

Fixes #7

EPSG/data/Overrides.js

@@ -1,8 +1,9 @@
 /**
  * Some parameters must be overridden or transformed in some way. This function performs all necessary transforms.
- * @param tokens
+ * @param tokens {Record<string, string | undefined | null>} Proj4 string tokens
+ * @param geoKeys {Record<string, number>} Geokeys
  */
-module.exports = function override(tokens) {
+module.exports = function override(tokens, geoKeys) {
 	let proj = tokens["+proj"], a = tokens["+a"], b = tokens["+b"];
 
 	// Some geokeys should be mapped to different Proj4 parameters than specified in PCSKeys.js
@@ -17,6 +18,15 @@ module.exports = function override(tokens) {
 		delete tokens["+lat_0"];
 	}
 
+	const crsCode = geoKeys.ProjectedCRSGeoKey || geoKeys.ProjectedCSTypeGeoKey;
+
+	// Web Mercator requires a sphere.
+	// Original CRS defines an ellipsoid for some reason, it also should be replaced with a sphere.
+	// See: https://github.com/matafokka/geotiff-geokeys-to-proj4/issues/7
+	if (crsCode === 3857 && tokens["+a"]) {
+		tokens["+b"] = tokens["+a"];
+	}
+
 	// These projections doesn't work with spheres, proj4 requires +approx parameter in this case
 	if (a === b && a !== undefined && (proj === "tmerc" || proj === "utm" || proj === "etmerc"))
 		tokens["+approx"] = null;

main.js

@@ -401,7 +401,7 @@ module.exports = {
 				tokens[kvArr[0].trim()] = kvArr[1].trim();
 		}
 
-		override(tokens); // Apply all necessary overrides
+		override(tokens, geoKeys); // Apply all necessary overrides
 
 		// Build final string
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "geotiff-geokeys-to-proj4",
-  "version": "2024.04.12",
+  "version": "2024.04.13",
   "description": "A library that converts GeoTIFFs geokeys to Proj4 string",
   "main": "main-dist.js",
   "module": "main-dist.mjs",

test.js

@@ -150,7 +150,18 @@ let testKeys = [
 		ProjLinearUnitsGeoKey: 9001,
 		VerticalCSTypeGeoKey: 8051,
 		proj4: "+proj=utm +zone=32 +datum=WGS84 +units=m +no_defs",
-	  }
+	},
+	{
+		name: "From #7",
+		GTModelTypeGeoKey: 1,
+		GTRasterTypeGeoKey: 1,
+		GTCitationGeoKey: "WGS 84 / Pseudo-Mercator",
+		GeogCitationGeoKey: "WGS 84",
+		GeogAngularUnitsGeoKey: 9102,
+		ProjectedCSTypeGeoKey: 3857,
+		ProjLinearUnitsGeoKey: 9001,
+		proj4: "+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs",
+	}
 ];
 
 // Test runner