Calculate boundingbox for point or multiple points

2015-12-17 00:22:52 +01:00
parent 48c4e72266
commit 358884f7d1
1 changed files with 79 additions and 0 deletions
@@ -0,0 +1,79 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Windows.Devices.Geolocation;
+
+namespace NavCityBreda.Helpers
+{
+    public class BoundingBox
+    {
+        public static GeoboundingBox GetBoundingBox(List<Geopoint> points)
+        {
+            double latitude_min = points.Select(p => p.Position.Latitude).Min();
+            double latitude_max = points.Select(p => p.Position.Latitude).Max();
+            double longitude_min = points.Select(p => p.Position.Longitude).Min();
+            double longitude_max = points.Select(p => p.Position.Longitude).Max();
+
+            return new GeoboundingBox(
+                new BasicGeoposition { Latitude = latitude_max, Longitude = longitude_max },
+                new BasicGeoposition { Latitude = latitude_min, Longitude = longitude_min }
+            );
+        }
+
+        // Semi-axes of WGS-84 geoidal reference
+        private const double WGS84_a = 6378137.0; // Major semiaxis [m]
+        private const double WGS84_b = 6356752.3; // Minor semiaxis [m]
+
+        // 'halfSideInKm' is the half length of the bounding box you want in kilometers.
+        public static GeoboundingBox GetBoundingBox(Geopoint point, double halfSideInKm)
+        {
+            // Bounding box surrounding the point at given coordinates,
+            // assuming local approximation of Earth surface as a sphere
+            // of radius given by WGS84
+            var lat = Deg2rad(point.Position.Latitude);
+            var lon = Deg2rad(point.Position.Longitude);
+            var halfSide = 1000 * halfSideInKm;
+
+            // Radius of Earth at given latitude
+            var radius = WGS84EarthRadius(lat);
+            // Radius of the parallel at given latitude
+            var pradius = radius * Math.Cos(lat);
+
+            var latMin = lat - halfSide / radius;
+            var latMax = lat + halfSide / radius;
+            var lonMin = lon - halfSide / pradius;
+            var lonMax = lon + halfSide / pradius;
+
+            return new GeoboundingBox(
+                new BasicGeoposition { Latitude = Rad2deg(latMax), Longitude = Rad2deg(lonMax) },
+                new BasicGeoposition { Latitude = Rad2deg(latMin), Longitude = Rad2deg(lonMin) }
+                
+             );
+        }
+
+        // degrees to radians
+        private static double Deg2rad(double degrees)
+        {
+            return Math.PI * degrees / 180.0;
+        }
+
+        // radians to degrees
+        private static double Rad2deg(double radians)
+        {
+            return 180.0 * radians / Math.PI;
+        }
+
+        // Earth radius at a given latitude, according to the WGS-84 ellipsoid [m]
+        private static double WGS84EarthRadius(double lat)
+        {
+            var An = WGS84_a * WGS84_a * Math.Cos(lat);
+            var Bn = WGS84_b * WGS84_b * Math.Sin(lat);
+            var Ad = WGS84_a * Math.Cos(lat);
+            var Bd = WGS84_b * Math.Sin(lat);
+            return Math.Sqrt((An * An + Bn * Bn) / (Ad * Ad + Bd * Bd));
+        }
+    }
+
+}