Minor improvements

MapControl/Shared/BoundingBox.cs

@@ -15,8 +15,8 @@ namespace MapControl
 #endif
     public class BoundingBox
     {
-        private double south;
-        private double north;
+        private double south = double.NaN;
+        private double north = double.NaN;
 
         public BoundingBox()
         {
@@ -30,9 +30,8 @@ namespace MapControl
             East = east;
         }
 
-        public double West { get; set; }
-
-        public double East { get; set; }
+        public double West { get; set; } = double.NaN;
+        public double East { get; set; } = double.NaN;
 
         public double South
         {
@@ -64,11 +63,16 @@ namespace MapControl
             protected set { }
         }
 
-        public static BoundingBox Parse(string s)
+        public static BoundingBox Parse(string boundingBox)
         {
-            var values = s.Split(new char[] { ',' });
+            string[] values = null;
 
-            if (values.Length != 4)
+            if (!string.IsNullOrEmpty(boundingBox))
+            {
+                values = boundingBox.Split(new char[] { ',' });
+            }
+
+            if (values?.Length != 4)
             {
                 throw new FormatException("BoundingBox string must be a comma-separated list of four floating point numbers.");
             }

MapControl/Shared/GroundOverlay.cs

@@ -242,11 +242,11 @@ namespace MapControl
 
         private static LatLonBox ReadLatLonBox(XmlElement element)
         {
-            double north = double.NaN;
-            double south = double.NaN;
-            double east = double.NaN;
-            double west = double.NaN;
-            double rotation = 0d;
+            var north = double.NaN;
+            var south = double.NaN;
+            var east = double.NaN;
+            var west = double.NaN;
+            var rotation = 0d;
 
             foreach (var childElement in element.ChildNodes.OfType<XmlElement>())
             {

MapControl/Shared/Location.cs

@@ -57,42 +57,33 @@ namespace MapControl
             return string.Format(CultureInfo.InvariantCulture, "{0:F5},{1:F5}", Latitude, Longitude);
         }
 
-        public static Location Parse(string locationString)
+        public static Location Parse(string location)
         {
-            Location location = null;
+            string[] values = null;
 
-            if (!string.IsNullOrEmpty(locationString))
+            if (!string.IsNullOrEmpty(location))
             {
-                var values = locationString.Split(new char[] { ',' });
-
-                if (values.Length != 2)
-                {
-                    throw new FormatException("Location string must be a comma-separated pair of double values.");
-                }
-
-                location = new Location(
-                    double.Parse(values[0], NumberStyles.Float, CultureInfo.InvariantCulture),
-                    double.Parse(values[1], NumberStyles.Float, CultureInfo.InvariantCulture));
+                values = location.Split(new char[] { ',' });
             }
 
-            return location;
+            if (values?.Length != 2)
+            {
+                throw new FormatException("Location string must be a comma-separated pair of floating point numbers.");
+            }
+
+            return new Location(
+                double.Parse(values[0], NumberStyles.Float, CultureInfo.InvariantCulture),
+                double.Parse(values[1], NumberStyles.Float, CultureInfo.InvariantCulture));
         }
 
         /// <summary>
-        /// Normalizes a longitude to a value in the interval [-180 .. 180].
+        /// Normalizes a longitude to a value in the interval [-180 .. 180).
         /// </summary>
         public static double NormalizeLongitude(double longitude)
         {
-            if (longitude < -180d)
-            {
-                longitude = ((longitude + 180d) % 360d) + 180d;
-            }
-            else if (longitude > 180d)
-            {
-                longitude = ((longitude - 180d) % 360d) - 180d;
-            }
+            var x = (longitude + 180d) % 360d;
 
-            return longitude;
+            return x < 0d ? x + 180d : x - 180d;
         }
 
         /// <summary>

MapControl/Shared/LocationCollection.cs

@@ -50,9 +50,14 @@ namespace MapControl
             Add(new Location(latitude, longitude));
         }
 
-        public static LocationCollection Parse(string s)
+        public static LocationCollection Parse(string locations)
         {
-            var strings = s.Split(new char[] { ' ', ';' }, StringSplitOptions.RemoveEmptyEntries);
+            if (string.IsNullOrEmpty(locations))
+            {
+                return new LocationCollection();
+            }
+
+            var strings = locations.Split(new char[] { ' ', ';' }, StringSplitOptions.RemoveEmptyEntries);
 
             return new LocationCollection(strings.Select(l => Location.Parse(l)));
         }

MapControl/Shared/MapBase.cs

@@ -390,11 +390,11 @@ namespace MapControl
 
             if (offset > 180d)
             {
-                longitude = Center.Longitude - 360d + offset % 360d;
+                longitude = Center.Longitude + (offset % 360d) - 360d;
             }
             else if (offset < -180d)
             {
-                longitude = Center.Longitude + 360d + offset % 360d;
+                longitude = Center.Longitude + (offset % 360d) + 360d;
             }
 
             return longitude;

MapControl/Shared/MapGraticule.cs

@@ -92,9 +92,7 @@ namespace MapControl
         {
             var hemisphere = hemispheres[0];
 
-            value = (value + 540d) % 360d - 180d;
-
-            if (value < -1e-8) // ~1mm
+            if (value < -1e-8) // ~1 mm
             {
                 value = -value;
                 hemisphere = hemispheres[1];

MapControl/Shared/MapPanel.cs

@@ -211,7 +211,6 @@ namespace MapControl
                 IsOutsideViewport(position))
             {
                 location = new Location(location.Latitude, parentMap.ConstrainedLongitude(location.Longitude));
-
                 position = parentMap.LocationToView(location);
             }
 

MapControl/Shared/MapProjection.cs

@@ -58,6 +58,7 @@ namespace MapControl
 
         /// <summary>
         /// Transforms a Location in geographic coordinates to a Point in projected map coordinates.
+        /// Returns new Point(double.NaN, double.NaN) when the Location can not be transformed.
         /// </summary>
         public abstract Point LocationToMap(Location location);
 

MapControl/Shared/ViewRect.cs

@@ -7,7 +7,7 @@ namespace MapControl
     /// <summary>
     /// Rotated rectangle used to arrange and rotate an element with a BoundingBox.
     /// </summary>
-    public struct ViewRect
+    public class ViewRect
     {
         public ViewRect(double x, double y, double width, double height, double rotation)
         {