How to use System.Spatial.GeographyPoint

Question

I need a function to calculate distance between point A and point B.

Namespace System.Spatial seems to be exactly what I need, but I can't figure how to use it.

IPoint is an interface that provides Latitude and Longitude, both of type double.

First try :

  public static double CalculateDistance(IPoint pointA, IPoint pointB)
  {
     var gp1 = GeographyPoint.Create(pointA.Latitude, pointA.Longitude);
     var gp2 = GeographyPoint.Create(pointB.Latitude, pointB.Longitude);

     return gp1.Distance(gp2) ?? 0;
  }

That ends with a NotImplementedExceptionon point1.Distance(point2). The message is in french, but basically it says "No operation registered. Please provide operation using property SpatialImplementation.CurrentImplementation.Operations".

Ok, I will try this then :

public static double CalculateDistance(IPoint pointA, IPoint pointB)
{
   var gp1 = GeographyPoint.Create(pointA.Latitude, pointA.Longitude);
   var gp2 = GeographyPoint.Create(pointB.Latitude, pointB.Longitude);

   return SpatialImplementation.CurrentImplementation.Operations.Distance(gp1, gp2);
}

Now I got a NullReferenceException on SpatialImplementation.CurrentImplementation.Operations.

Msdn is not much verbose about this.

Anyone can explain how to get these implementations ?

Answer 1

IMHO you shouldn't use System.Spatial. It's an half-baked library created for OData interoperability with Spatial, namely for WCF Data-Services.

You can check here for more information. Also, most of the classes on that library are abstract, hence up-to-you to be implement most-of-it.

Also, and even worse, they're incompatible with Entity Framework spatial support.

I'm not sure what kind of project you're on but I would suggest these guidelines:

• if you just need to calculate distances between points just copy an implementation of the Haversine Formula or Vincenty's Formula in C#.

• if you need spatial on DB just go with Entity Framework 5/6.

• if you need further spatial operations in c# use something like NetTopologySuite. There's a NuGet for it and it's really simple to use.