using System; namespace Xamarin.Forms.Maps { public sealed class MapSpan { const double EarthRadiusKm = 6371; const double EarthCircumferenceKm = EarthRadiusKm * 2 * Math.PI; const double MinimumRangeDegrees = 0.001 / EarthCircumferenceKm * 360; // 1 meter public MapSpan(Position center, double latitudeDegrees, double longitudeDegrees) { Center = center; LatitudeDegrees = Math.Min(Math.Max(latitudeDegrees, MinimumRangeDegrees), 90.0); LongitudeDegrees = Math.Min(Math.Max(longitudeDegrees, MinimumRangeDegrees), 180.0); } public Position Center { get; } public double LatitudeDegrees { get; } public double LongitudeDegrees { get; } public Distance Radius { get { double latKm = LatitudeDegreesToKm(LatitudeDegrees); double longKm = LongitudeDegreesToKm(Center, LongitudeDegrees); return new Distance(1000 * Math.Min(latKm, longKm) / 2); } } public MapSpan ClampLatitude(double north, double south) { north = Math.Min(Math.Max(north, 0), 90); south = Math.Max(Math.Min(south, 0), -90); double lat = Math.Max(Math.Min(Center.Latitude, north), south); double maxDLat = Math.Min(north - lat, -south + lat) * 2; return new MapSpan(new Position(lat, Center.Longitude), Math.Min(LatitudeDegrees, maxDLat), LongitudeDegrees); } public override bool Equals(object obj) { if (ReferenceEquals(null, obj)) return false; if (ReferenceEquals(this, obj)) return true; return obj is MapSpan && Equals((MapSpan)obj); } public static MapSpan FromCenterAndRadius(Position center, Distance radius) { return new MapSpan(center, 2 * DistanceToLatitudeDegrees(radius), 2 * DistanceToLongitudeDegrees(center, radius)); } public override int GetHashCode() { unchecked { int hashCode = Center.GetHashCode(); hashCode = (hashCode * 397) ^ LongitudeDegrees.GetHashCode(); hashCode = (hashCode * 397) ^ LatitudeDegrees.GetHashCode(); return hashCode; } } public static bool operator ==(MapSpan left, MapSpan right) { return Equals(left, right); } public static bool operator !=(MapSpan left, MapSpan right) { return !Equals(left, right); } public MapSpan WithZoom(double zoomFactor) { double maxDLat = Math.Min(90 - Center.Latitude, 90 + Center.Latitude) * 2; return new MapSpan(Center, Math.Min(LatitudeDegrees / zoomFactor, maxDLat), LongitudeDegrees / zoomFactor); } static double DistanceToLatitudeDegrees(Distance distance) { return distance.Kilometers / EarthCircumferenceKm * 360; } static double DistanceToLongitudeDegrees(Position position, Distance distance) { double latCircumference = LatitudeCircumferenceKm(position); return distance.Kilometers / latCircumference * 360; } bool Equals(MapSpan other) { return Center.Equals(other.Center) && LongitudeDegrees.Equals(other.LongitudeDegrees) && LatitudeDegrees.Equals(other.LatitudeDegrees); } static double LatitudeCircumferenceKm(Position position) { return EarthCircumferenceKm * Math.Cos(position.Latitude * Math.PI / 180.0); } static double LatitudeDegreesToKm(double latitudeDegrees) { return EarthCircumferenceKm * latitudeDegrees / 360; } static double LongitudeDegreesToKm(Position position, double longitudeDegrees) { double latCircumference = LatitudeCircumferenceKm(position); return latCircumference * longitudeDegrees / 360; } } }