Operand type clash geography is incompatible with float

Question

I am trying to figure out how to build a function that measures the distance from one location to another in miles, using longitude and latitude. The parameters would be added when EXECUTE is run. I am trying to do this using the "geography::Point()" and the "STDistance" instead of float.

IF OBJECT_ID('dbo.udfDistanceMiles') IS NOT NULL
  DROP FUNCTION dbo.udfDistanceMiles
GO
CREATE FUNCTION dbo.udfDistanceMiles 
(
    @long1 geography,
    @long2 geography,
    @lat1 geography,
    @lat2 geography
)
RETURNS geography
AS
BEGIN
    DECLARE @from geography
    DECLARE @to geography
    DECLARE @kilo geography
    DECLARE @miles as geography

    SET @from = geography::Point(@lat1,@long1,4268);
    SET @to = geography::Point(@lat2,@long2,4268);
    SET @kilo = (SELECT @from.STDistance(@to));
        BEGIN
            SET @miles = (@kilo * '.621371');
        END 

    RETURN @miles

END
GO

This is an assignment for a class I am taking on spatial databases, but I've run into a snag that I cannot figure out. I am running into this Operand type clash when trying to just create the function:

Msg 206, Level 16, State 2, Procedure udfDistanceMiles, Line 19
Operand type clash: geography is incompatible with float
Msg 206, Level 16, State 2, Procedure udfDistanceMiles, Line 19
Operand type clash: geography is incompatible with float
Msg 206, Level 16, State 2, Procedure udfDistanceMiles, Line 20
Operand type clash: geography is incompatible with float
Msg 206, Level 16, State 2, Procedure udfDistanceMiles, Line 20
Operand type clash: geography is incompatible with float
Msg 206, Level 16, State 2, Procedure udfDistanceMiles, Line 21
Operand type clash: float is incompatible with geography
Msg 403, Level 16, State 1, Procedure udfDistanceMiles, Line 23
Invalid operator for data type. Operator equals multiply, type equals geography.

Any help for a newb would be appreciated.

Thanks

John

Answer 1

Here is the finished Function that worked for me, along with its EXEC to measure miles from SLC, UT to LA, CA.

ALTER FUNCTION [dbo].[udfDistanceMiles] 
(
    @long1 float,
    @long2 float,
    @lat1 float,
    @lat2 float
)
RETURNS float
AS
BEGIN
    DECLARE @from geography
    DECLARE @to geography
    DECLARE @miles as float

    SET @from = geography::Point(@lat1,@long1,4326);
    SET @to = geography::Point(@lat2,@long2,4326);
    SET @miles = (SELECT ((@from.STDistance(@to) * '.001') * '.621371'));
    --SET @miles = (SELECT (@from.STDistance(@to) * '.621371'));

    RETURN @miles

END

And the EXEC:

USE DBM384;
GO

DECLARE @miles float= NULL;

EXEC @miles = dbo.udfDistanceMiles @lat1= 34, @long1= -118, @lat2= 40.758701, @long2= -111.876183;

PRINT @miles;