Fixed moving transform center across dateline.

MapControl/Shared/BoundingBox.cs

@@ -30,12 +30,6 @@ namespace MapControl
             East = east;
         }
 
-        public BoundingBox(BoundingBox boundingBox, double longitudeOffset)
-            : this(boundingBox.South, boundingBox.West + longitudeOffset,
-                   boundingBox.North, boundingBox.East + longitudeOffset)
-        {
-        }
-
         public double West { get; set; }
 
         public double East { get; set; }

MapControl/Shared/MapBase.cs

@@ -272,7 +272,8 @@ namespace MapControl
 
         /// <summary>
         /// Sets a temporary center point in view coordinates for scaling and rotation transformations.
-        /// This center point is automatically reset when the Center property is set by application code.
+        /// This center point is automatically reset when the Center property is set by application code
+        /// or by the methods TranslateMap, TransformMap, ZoomMap and ZoomToBounds.
         /// </summary>
         public void SetTransformCenter(Point center)
         {
@@ -728,6 +729,7 @@ namespace MapControl
 
         private void UpdateTransform(bool resetTransformCenter = false, bool projectionChanged = false)
         {
+            var transformCenterChanged = false;
             var viewScale = ViewTransform.ZoomLevelToScale(ZoomLevel);
             var projection = MapProjection;
 
@@ -762,6 +764,9 @@ namespace MapControl
 
                         if (resetTransformCenter)
                         {
+                            // check if transform center moved across the dateline
+                            transformCenterChanged = Math.Abs(center.Longitude - transformCenter.Longitude) > 180d;
+
                             ResetTransformCenter();
 
                             projection.Center = ProjectionCenter ?? Center;
@@ -778,9 +783,11 @@ namespace MapControl
 
                 SetViewScale(ViewTransform.Scale);
 
-                OnViewportChanged(new ViewportChangedEventArgs(projectionChanged, Center.Longitude - centerLongitude));
+                // check if view center moved across the dateline
-
+                transformCenterChanged = transformCenterChanged || Math.Abs(Center.Longitude - centerLongitude) > 180d;
                 centerLongitude = Center.Longitude;
+
+                OnViewportChanged(new ViewportChangedEventArgs(projectionChanged, transformCenterChanged));
             }
         }
 

MapControl/Shared/MapImageLayer.cs

@@ -171,11 +171,11 @@ namespace MapControl
 
                 base.OnViewportChanged(e);
 
-                await UpdateImageAsync();
+                await UpdateImageAsync(); // update immediately
             }
             else
             {
-                AdjustBoundingBox(e.LongitudeOffset);
+                ValidateBoundingBox();
 
                 base.OnViewportChanged(e);
 
@@ -233,21 +233,30 @@ namespace MapControl
             BoundingBox = ParentMap.ViewRectToBoundingBox(rect);
         }
 
-        private void AdjustBoundingBox(double longitudeOffset)
+        private void ValidateBoundingBox()
         {
-            if (Math.Abs(longitudeOffset) > 180d && BoundingBox != null)
+            if (BoundingBox != null)
             {
-                var offset = 360d * Math.Sign(longitudeOffset);
+                var offset = ParentMap.Center.Longitude - BoundingBox.Center.Longitude;
 
-                BoundingBox = new BoundingBox(BoundingBox, offset);
+                if (Math.Abs(offset) > 180d)
+                {
+                    offset = 360d * Math.Sign(offset);
+
+                    BoundingBox = new BoundingBox(
+                        BoundingBox.South, BoundingBox.West + offset,
+                        BoundingBox.North, BoundingBox.East + offset);
 
                     foreach (var image in Children.OfType<Image>())
                     {
-                    var imageBoundingBox = GetBoundingBox(image);
+                        var imageBbox = GetBoundingBox(image);
 
-                    if (imageBoundingBox != null)
+                        if (imageBbox != null)
                         {
-                        SetBoundingBox(image, new BoundingBox(imageBoundingBox, offset));
+                            SetBoundingBox(image, new BoundingBox(
+                                imageBbox.South, imageBbox.West + offset,
+                                imageBbox.North, imageBbox.East + offset));
+                        }
                     }
                 }
             }

MapControl/Shared/MapTileLayer.cs

@@ -3,6 +3,7 @@
 // Licensed under the Microsoft Public License (Ms-PL)
 
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 #if WINUI
 using Windows.Foundation;
@@ -125,11 +126,11 @@ namespace MapControl
 
         protected override Task UpdateTileLayer()
         {
-            var update = false;
+            var updateTiles = false;
 
             if (ParentMap == null || ParentMap.MapProjection.Type != MapProjectionType.WebMercator)
             {
-                update = TileMatrix != null;
+                updateTiles = TileMatrix != null;
                 TileMatrix = null;
             }
             else
@@ -137,27 +138,23 @@ namespace MapControl
                 if (TileSource != TileImageLoader.TileSource)
                 {
                     Tiles = new TileCollection(); // clear all
-                    update = true;
+                    updateTiles = true;
                 }
 
                 if (SetTileMatrix())
                 {
+                    updateTiles = true;
+                }
+
                 SetRenderTransform();
-                    update = true;
-                }
             }
 
-            if (update)
+            return updateTiles ? UpdateTiles() : Task.CompletedTask;
-            {
-                UpdateTiles();
-
-                return TileImageLoader.LoadTiles(Tiles, TileSource, SourceName);
-            }
-
-            return Task.CompletedTask;
         }
 
         protected override void SetRenderTransform()
+        {
+            if (TileMatrix != null)
             {
                 // tile matrix origin in pixels
                 //
@@ -168,6 +165,7 @@ namespace MapControl
                 ((MatrixTransform)RenderTransform).Matrix =
                     ParentMap.ViewTransform.GetTileLayerTransform(tileMatrixScale, MapTopLeft, tileMatrixOrigin);
             }
+        }
 
         private bool SetTileMatrix()
         {
@@ -199,7 +197,7 @@ namespace MapControl
             return true;
         }
 
-        private void UpdateTiles()
+        private Task UpdateTiles()
         {
             var tiles = new TileCollection();
 
@@ -241,6 +239,8 @@ namespace MapControl
             {
                 Children.Add(tile.Image);
             }
+
+            return TileImageLoader.LoadTiles(tiles, TileSource, SourceName);
         }
     }
 }

MapControl/Shared/MapTileLayerBase.cs

@@ -201,9 +201,9 @@ namespace MapControl
 
         private async void OnViewportChanged(object sender, ViewportChangedEventArgs e)
         {
-            if (Children.Count == 0 || e.ProjectionChanged || Math.Abs(e.LongitudeOffset) > 180d)
+            if (Children.Count == 0 || e.ProjectionChanged || e.TransformCenterChanged)
             {
-                await Update(); // update immediately when projection has changed or center has moved across 180° longitude
+                await Update(); // update immediately
             }
             else
             {

MapControl/Shared/ViewportChangedEventArgs.cs

@@ -8,22 +8,23 @@ namespace MapControl
 {
     public class ViewportChangedEventArgs : EventArgs
     {
-        public ViewportChangedEventArgs(bool projectionChanged = false, double longitudeOffset = 0d)
+        public ViewportChangedEventArgs(bool projectionChanged = false, bool transformCenterChanged = false)
         {
             ProjectionChanged = projectionChanged;
-            LongitudeOffset = longitudeOffset;
+            TransformCenterChanged = transformCenterChanged;
         }
 
         /// <summary>
-        /// Indicates if the map projection has changed. Used to control when a MapTileLayer or MapImageLayer
+        /// Indicates that the map projection has changed. Used to control when
-        /// should be updated immediately, or MapPath Data in projected map coordinates should be recalculated.
+        /// a MapTileLayer or a MapImageLayer should be updated immediately,
+        /// or MapPath Data in projected map coordinates should be recalculated.
         /// </summary>
         public bool ProjectionChanged { get; }
 
         /// <summary>
-        /// Offset of the map center longitude value from the previous viewport.
+        /// Indicates that the view transform center has moved across the dateline.
-        /// Used to detect if the map center has moved across 180° longitude.
+        /// Used to control when a MapTileLayer should be updated immediately.
         /// </summary>
-        public double LongitudeOffset { get; }
+        public bool TransformCenterChanged { get; }
     }
 }

MapControl/Shared/WmtsTileLayer.cs

@@ -94,14 +94,11 @@ namespace MapControl
                 return UpdateTiles(null);
             }
 
-            if (UpdateChildLayers(tileMatrixSet))
+            var updateTiles = UpdateChildLayers(tileMatrixSet);
-            {
+
             SetRenderTransform();
 
-                return UpdateTiles(tileMatrixSet);
+            return updateTiles ? UpdateTiles(tileMatrixSet) : Task.CompletedTask;
-            }
-
-            return Task.CompletedTask;
         }
 
         protected override void SetRenderTransform()