Posted by Philip Leitch Monday, March 8, 2010 10:37:37 PM Categories: Geospatial Scalar Function
CREATE function [dbo].[Distance]
(@Lat1 float, @Long1 float, @Lat2 float, @Long2 float)
Author: Philip Leitch
Date: 2010
Purpose: This function measures the distance between two geospatial points.
Copyright: Philip Leitch 2010
Licensing: This code may be used or modified but if the code is included in a software package attribution to me must be made.
Liability: The developer assumes all liability when using this code.
Based on the "ellipsoidal Vincenty formula".  This might not be quite as accurate as others, but is close on accuracy and very fast.
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The result is in kilometres Multiply by 1000 for metres

returns float

    if abs(@lat1 - @lat2) < 0.00001 and abs(@long1 - @long2) < 0.00001
        return 0
    Declare @Radius float
    set @Radius = dbo.Earth_Radius((@lat1 + @lat2)/cast(2 as float))

    --Convert to radians
    set @Lat1 = @lat1 * (pi()/180)   
    set @Long1 = @long1 * (pi()/180)   
    set @Lat2 = @lat2 * (pi()/180)   
    set @Long2 = @long2 * (pi()/180)   
    Declare @return float
    set @return = acos(
    Cos(@Lat1) * cos(@Long1) *
    Cos(@Lat2) * cos(@Long2) +
    cos(@lat1) * sin(@Long1) *
    cos(@lat2) * sin(@Long2) +
    sin(@lat1) * sin(@lat2)
    ) * @Radius

    return @return
Copyright 2009 Philip Leitch


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