Distance between 2 geocodes

Question

What is the formula for calculating the distance between 2 geocodes? I have seen some of the answers on this site but they basically say to rely on SQL Server 08 functions,

Answer 1

You're looking for the length of the Great Circle Path between two points on a sphere. Try looking up "Great Circle Path" or "Great Circle Distance" on Google.

Answer 2

the pythagorean theorem?

Answer 3

Use an approximation of the earth and the Haversine formula. You can get a javascript version on the following url, which you can translate to your language of choice:

http://www.movable-type.co.uk/scripts/latlong.html

Here is another way: http://escience.anu.edu.au/project/04S2/SE/3DVOT/3DVOT/pHatTrack_Application/Source_code/pHatTrack/Converter.java

Answer 4

Here is a way to do it if you are using sql server.

CREATE function dist (@Lat1 varchar(50), @Lng1 varchar(50),@Lat2 varchar(50), @Lng2 varchar(50)) 
returns float 
as
begin

declare @p1 geography
declare @p2 geography

set @p1 = geography::STGeomFromText('POINT('+ @Lng1+' '+ @Lat1 +')', 4326)
set @p2 = geography::STGeomFromText('POINT('+ @Lng2+' '+ @Lat2 +')', 4326)

return @p1.STDistance(@p2)
end

Answer 5

This will do it for you in c#.

Within the namespace put these:

 public enum DistanceType { Miles, Kilometers };

public struct Position
{
    public double Latitude;
    public double Longitude;
}

class Haversine
{

    public double Distance(Position pos1, Position pos2, DistanceType type)
    {
        double preDlat = pos2.Latitude - pos1.Latitude;
        double preDlon = pos2.Longitude - pos1.Longitude;
        double R = (type == DistanceType.Miles) ? 3960 : 6371;
        double dLat = this.toRadian(preDlat);
        double dLon = this.toRadian(preDlon);
        double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2) +
        Math.Cos(this.toRadian(pos1.Latitude)) * Math.Cos(this.toRadian(pos2.Latitude)) *
        Math.Sin(dLon / 2) * Math.Sin(dLon / 2);
        double c = 2 * Math.Asin(Math.Min(1, Math.Sqrt(a)));
        double d = R * c;
        return d;
    }

    private double toRadian(double val)
    {
        return (Math.PI / 180) * val;
    }

Then to utilise these in the main code:

Position pos1 = new Position();
                    pos1.Latitude = Convert.ToDouble(hotelx.latitude);
                    pos1.Longitude = Convert.ToDouble(hotelx.longitude);
                    Position pos2 = new Position();
                    pos2.Latitude = Convert.ToDouble(lat);
                    pos2.Longitude = Convert.ToDouble(lng);
                    Haversine calc = new Haversine();

                    double result = calc.Distance(pos1, pos2, DistanceType.Miles);

Answer 6

Sorry, I don't know what country you are in even. Are we talking about Easting and Northings (UK, Ordance Survey system) or Lat/Long or some other system? If we are talking Easting and Northing then you can use
sqr((x1-x2)^2 + (y1-y2)^2)
This does not allow for the fact that the earth is a sphere, but for short distances you won't notice. We use it at work for distances between points within the county.
Be carful about how longer grid reference you use. I think an 8 figure reference will give you a distance in metres. I'll be able to get a definate answer at work next week if no one else has supplied it.