SQL Server Spatial Data - Working with Circles

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SQL Server Spatial Data - Working with Circles

chris.king

SSCrazy

Points: 2007
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July 15, 2014 at 2:24 am

#293291

Hi there,
I am not very familiar with working with spatial data and I am currently trying to work out how to obtain some properties of a circle defined as a geometry data type.
Specifically, I need to determine x and y co-ordinates for the centre point and the diameter of the circle.
I have had a look at the MSDN reference for spatial data and done some general googling but I must admit I am struggling to find anything relevant.
Any advice or guidance would be greatly appreciated.
TIA,
Chris

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Eirikur Eiriksson SSC Guru Points: 182911 More actions · Answer 1

Simplest method is to use STBuffer, the parameter passed is effectively the radius.

😎

DECLARE @circle GEOMETRY = geometry::Point(1.00,1.00,0).STBuffer(1);

SELECT @circle

chris.king SSCrazy Points: 2007 More actions · Answer 2

Hi,

Thanks for your reply.

If I understand correctly, I would need the centre point in order to use STBuffer().

I don't currently understand how to find the centre point from the existing shape stored as a CIRCULARSTRING. Here is some example data I am working with:

CIRCULARSTRING (52.6107417597068 -1.19053984363516, 52.6107417597068 -1.19185949047026, 52.6114844449159 -1.19185949047026, 52.6114844449159 -1.19053984363516, 52.6107417597068 -1.19053984363516)

CIRCULARSTRING (0 4, 4 0, 8 4, 4 8, 0 4)

Based on this, is there an easy way to find the centre point?

TIA,

Chris

Eirikur Eiriksson SSC Guru Points: 182911 More actions · Answer 3

This should get you started, find where lines drawn between every other point defining the circle crosses

😎

USE tempdb;

GO

DECLARE @circle GEOMETRY = 'CIRCULARSTRING (52.6107417597068 -1.19053984363516, 52.6107417597068 -1.19185949047026, 52.6114844449159 -1.19185949047026, 52.6114844449159 -1.19053984363516, 52.6107417597068 -1.19053984363516)'

;WITH T(N) AS (SELECT X.N FROM (VALUES (NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)) AS X(N))

,NUMS(N) AS (SELECT TOP(@CIRCLE.STNumPoints() - 1 ) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS N FROM T T1,T,T T2,T T3,T T4)

,C_POINTS AS

(

SELECT

NM.N AS POINT_NO

,@CIRCLE.STPointN(N) /*.STBuffer(0.0001)*/ AS POINT_GEO

FROM NUMS NM

)

SELECT

C1.POINT_GEO.ShortestLineTo(C3.POINT_GEO).STIntersection(C2.POINT_GEO.ShortestLineTo(C4.POINT_GEO)).STBuffer(0.0001)

FROM C_POINTS C1

CROSS APPLY C_POINTS C2

CROSS APPLY C_POINTS C3

CROSS APPLY C_POINTS C4

WHERE C1.POINT_NO = 1

AND C2.POINT_NO = 2

AND C3.POINT_NO = 3

AND C4.POINT_NO = 4

UNION ALL

SELECT @circle

chris.king SSCrazy Points: 2007 More actions · Answer 4

Hi Thanks,

I'll have play around with the code supplied.

Thanks for the help 😉

Chris