Question

Here is my code.

Create Table [dbo].[MajorCities]
(
[CityID] int Identity(1,1),
[CityName] varchar(60),
[Latitude] float,
[Longitude] float,
GeoRef Geography
)

INSERT INTO dbo.[MajorCities] values
 ('New Delhi, India', 28.6, 77.2, null),
 ('Paris, France', 48.86667, 2.3333, null),
 ('Rio de Janeiro, Brazil', -22.9, -43.23333, null),
 ('Sydney, Australia', -33.88306, 151.21667, null),
('New York City, USA', 40.78333, -73.96667, null)

select * from [MajorCities]


UPDATE [dbo].[MajorCities]
SET [GeoRef] = geography::STPointFromText ('POINT (' + CAST ([Longitude] AS VARCHAR (20)) + ' ' +
                    CAST ([Latitude] AS VARCHAR (20)) + ')', 4326)

I want to find the distance between two locations in KM.

Please help me.
Thanks.

Answer 1

If you have your Latitude and Longitude in form of degrees (just like in your table), then you may use the following function:

CREATE FUNCTION dbo.DictanceKM(@lat1 FLOAT, @lat2 FLOAT, @lon1 FLOAT, @lon2 FLOAT)
RETURNS FLOAT 
AS
BEGIN

    RETURN ACOS(SIN(PI()*@lat1/180.0)*SIN(PI()*@lat2/180.0)+COS(PI()*@lat1/180.0)*COS(PI()*@lat2/180.0)*COS(PI()*@lon2/180.0-PI()*@lon1/180.0))*6371
END

OR if you insist on Geography type, usage is:

DECLARE @g geography;
DECLARE @h geography;
SET @g = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326);
SET @h = geography::STGeomFromText('POINT(-122.34900 47.65100)', 4326);
SELECT @g.STDistance(@h);