Added GeoApiProjectionFactory

MapProjections/Shared/GeoApiProjectionFactory.cs

@@ -0,0 +1,70 @@
+// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
+// © 2022 Clemens Fischer
+// Licensed under the Microsoft Public License (Ms-PL)
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Net.Http;
+
+namespace MapControl.Projections
+{
+    public class GeoApiProjectionFactory : MapProjectionFactory
+    {
+        private readonly Dictionary<int, string> wkts = new Dictionary<int, string>();
+        private readonly HttpClient httpClient = new HttpClient();
+
+        public override MapProjection CreateProjection(string projectionDefinition)
+        {
+            var projection = base.CreateProjection(projectionDefinition);
+
+            if (projection == null &&
+                projectionDefinition.StartsWith("EPSG:") &&
+                int.TryParse(projectionDefinition.Substring(5), out int epsgCode))
+            {
+                if (epsgCode >= 32601 && epsgCode <= 32660)
+                {
+                    projection = new UtmProjection(epsgCode - 32600, true);
+                }
+                else if (epsgCode == 32661)
+                {
+                    projection = new UpsNorthProjection();
+                }
+                else if (epsgCode >= 32701 && epsgCode <= 32760)
+                {
+                    projection = new UtmProjection(epsgCode - 32700, false);
+                }
+                else if (epsgCode == 32761)
+                {
+                    projection = new UpsSouthProjection();
+                }
+                else
+                {
+                    projection = new GeoApiProjection(GetWkt(epsgCode));
+                }
+            }
+
+            return projection;
+        }
+
+        private string GetWkt(int epsgCode)
+        {
+            if (!wkts.TryGetValue(epsgCode, out string wkt))
+            {
+                var url = string.Format("https://epsg.io/{0}.wkt", epsgCode);
+
+                try
+                {
+                    wkt = httpClient.GetStringAsync(url).Result; // potential deadlock?
+                    wkts[epsgCode] = wkt;
+                }
+                catch (Exception ex)
+                {
+                    Debug.WriteLine($"GeoApiProjectionFactory.GetWkt({epsgCode}): {url}: {ex.Message}");
+                }
+            }
+
+            return wkt;
+        }
+    }
+}