DbGeography Reverse Polygon Point Order (Ring Orientation) With Entity Framework 5, WKTString and MSSQL 2008

Mar 18, 2013
entity frameworks
1 min read

If you draw a polygon using Google maps in a clock wise direction and then try to create a DbGeography object from the Well Known Text String (WKTString) it will create a polygon that covers the area of the earth EXCEPT the area you drew on the map.

To reverse the Polygon Point Order (Ring Orientation), you can use the following code:

using Microsoft.SqlServer.Types; 
using System; 
using System.Collections.Generic; 
using System.Data.Spatial; 
using System.Data.SqlTypes; 
namespace SomeNamespace 
{ 
    public static class DbGeographyHelper 
    { 
        // 4326 is most common coordinate system used by GPS/Maps 
        // 4326 format puts LONGITUDE first then LATITUDE 
        private static int _coordinateSystem = 4326; 
        public static DbGeography CreatePolygon(string wktString) 
        { 
            var sqlGeography = SqlGeography.STGeomFromText(new SqlChars(wktString), _coordinateSystem) .MakeValid(); 
            var invertedSqlGeography = sqlGeography.ReorientObject(); 
            if (sqlGeography.STArea() > invertedSqlGeography.STArea()) 
            { 
                sqlGeography = invertedSqlGeography; 
            } 
            return DbSpatialServices.Default.GeographyFromProviderValue(sqlGeography); 
        } 
    }
}

I got the idea from this great post