Question

I’ve got the following problem:
I have a table with long/lat values and another table with a project-id and long/lat/radius (circle).

Now I need to find out which project matches the long/lat values from the first table.

Is there an easy way to do that?

Answer 1

There are multiple algorithms to calculate distance on sphere, but we use following:

create function GetDistance(
    @latitudeFrom decimal(30,10), 
    @longitudeFrom decimal(30,10),
    @latitudeTo decimal(30,10), 
    @longitudeTo decimal(30,10)
)
RETURNS float
AS
BEGIN

DECLARE @distance float

    SET @distance = ROUND(6378.137 * ACOS(
            convert(decimal(30,10), 
            (SIN(RADIANS(@latitudeFrom)) * SIN(RADIANS(@latitudeTo))) +
            (COS(RADIANS(@latitudeFrom)) * COS(RADIANS(@latitudeTo)) *
             COS(RADIANS(@longitudeTo) - RADIANS(@longitudeFrom))))), 15)

 RETURN @distance
 END
 go

(where 6378.137 – is Earth’s radius)

So now when you can calculate distance between 2 points on Earth you can build query

 select * 
     from Table1, Project 
     where dbo.GetDistance(
           Table1.lat, Table1.lon, 
           Project.lat, Project.lon) < @YouRadius

where @YouRadius – parameterized radius of your circle