Find Closest Location from longitude and latitude within Sql database using Linq

FindClosesLocation.cs

var constValue = 57.2957795130823D

var constValue2 = 3958.75586574D;

var searchWithin = 20;

double latitude = ConversionHelper.SafeConvertToDoubleCultureInd(Latitude, 0),
                    longitude = ConversionHelper.SafeConvertToDoubleCultureInd(Longitude, 0);
var loc = (from l in DB.locations
            let temp = Math.Sin(Convert.ToDouble(l.Latitude) / constValue) 
            *  Math.Sin(Convert.ToDouble(latitude) / constValue) 
            +  Math.Cos(Convert.ToDouble(l.Latitude) / constValue) 
            *  Math.Cos(Convert.ToDouble(latitude) / constValue) 
            *  Math.Cos((Convert.ToDouble(longitude) / constValue) 
            - (Convert.ToDouble(l.Longitude) / constValue))
                    let calMiles = (constValue2 * Math.Acos(temp > 1 ? 1 : (temp < -1 ? -1 : temp)))
                    where (l.Latitude > 0 && l.Longitude > 0)
                    orderby calMiles
                    select new location
                      {
                         Name = l.name
                      });
                      return loc .ToList();

My code ;)

https://stackoverflow.com/questions/12835851/find-closest-location-with-longitude-and-latitude/12860259?noredirect=1#comment80313131_12860259

(y)

How to reference ConversionHelper?

Also how to get just first record back with the nearest location?

@apixu I have never used this code myself, was just collecting references how to calculate distance in various solutions. Later I resolved to use storedprocedure in MS SQL. In other database like MongoDB they have built in Geo function. But if you are using this code, I think you can avoid using ConversionHelper if you have Latitude already in double type but if it is string you can use Double.TryParse method.
To get first value in Linq you can use .First() method.

what constValue? why u need that?