SQL Server: Calculate the Radius of a Lat/Long? - sql-server

Question

Say I have the latitude and longitude of a city and I need to find out all the airport that are within 100 miles of this location. How would I accomplish this? My data resides in SQL Server. 1 table has all the city info with lat and long and the other has the airport info with lat and long.

Answer 1

First ... convert city's data point
DECLARE #point geography;
SELECT geography::STPointFromText('POINT(' + CAST(#lat AS VARCHAR(20)) + ' ' +
CAST(#lon AS VARCHAR(20)) + ')', 4326)
where #lat and #lon are the latitude and longitude of the city in question.
Then you can query the table ...
SELECT [column1],[column2],[etc]
FROM [table]
WHERE #point.STBuffer(160934.4).STIntersects(geography::STPointFromText(
'POINT(' + CAST([lat] AS VARCHAR(20)) + ' ' +
CAST([lon] AS VARCHAR(20)) + ')', 4326) );
where 160934.4 is the number of meters in 100 miles.
This will be slow, though. If you wanted to do even more spatial work, you could add a persisted computed column (because lat and lon points aren't really going to change) and then use a spatial index.
ALTER TABLE [table]
ADD geo_point AS geography::STPointFromText('POINT(' + CAST([lat] AS VARCHAR(20))
+ ' ' + CAST([lon] AS VARCHAR(20)) + ')', 4326) PERSISTED;
CREATE SPATIAL INDEX spix_table_geopt
ON table(geo_point)
WITH ( BOUNDING_BOX = ( 0, 0, 500, 200 ) ); --you'd have to know your data

Answer 2

I used/wrote this several years ago, and it was close enough for what I needed. Part of the formula takes into account the curvature of the earth if I remember correctly, but it has been a while. I used zip codes, but you could easily adapt for cities instead - same logic.
ALTER PROCEDURE [dbo].[sp_StoresByZipArea] (#zip nvarchar(5), #Radius float) AS
DECLARE #LatRange float
DECLARE #LongRange float
DECLARE #LowLatitude float
DECLARE #HighLatitude float
DECLARE #LowLongitude float
DECLARE #HighLongitude float
DECLARE #istartlat float
DECLARE #istartlong float
SELECT #iStartlat=Latitude, #iStartLong=Longitude from zipcodes where zipcode=#ZIP
SELECT #LatRange = #Radius / ((6076 / 5280) * 60)
SELECT #LongRange = #Radius / (((cos((#iStartLat * 3.141592653589 / 180)) * 6076.) / 5280.) * 60)
SELECT #LowLatitude = #istartlat - #LatRange
SELECT #HighLatitude = #istartlat + #LatRange
SELECT #LowLongitude = #istartlong - #LongRange
SELECT #HighLongitude = #istartlong + #LongRange
/** Now you can create a SQL statement which limits the recordset of cities in this manner: **/
SELECT * FROM ZipCodes
WHERE (Latitude <= #HighLatitude) AND (Latitude >= #LowLatitude) AND (Longitude >= #LowLongitude) AND (Longitude <= #HighLongitude)