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BufferWithCurves (geometry Data Type)

Returns a geometry instance that represents the set of all points whose distance from the calling geometry instance is less than or equal to the distance parameter.

Applies to: SQL Server (SQL Server 2012 through current version), Azure SQL Database.

.BufferWithCurves ( distance )

distance

Is a float indicating the maximum distance that points forming the buffer can be from the geometry instance.

SQL Server return type: geometry

CLR return type: SqlGeometry

The following criteria will throw an ArgumentException.

  • No parameter is passed to the method, such as @g.BufferWithCurves()

  • A non-numeric parameter is passed to the method, such as @g.BufferWithCurves('a')

  • NULL is passed to the method, such as @g.BufferWithCurves(NULL)

The following illustration shows an example of a geometry instance returned by this method.

BufferedCurve

The following table shows the results returned for different distance values.

distance Value

Type Dimensions

Spatial Type Returned

distance < 0

Zero or One

Empty GeometryCollection instance

distance < 0

Two or More

A CurvePolygon or GeometryCollection instance with a negative buffer

Note Note

A negative buffer may create an empty GeometryCollection

distance = 0

All dimensions

Copy of the invoking geometry instance

distance > 0

All dimensions

CurvePolygon or GeometryCollection instance

Note Note

Since distance is a float, a very small value can equate to zero in the calculations. When this occurs then a copy of the calling geometry instance is returned. See float and real (Transact-SQL).

A negative buffer removes all points enclosed in the given distance of the boundary of the geometry. The following illustration shows a negative buffer as the lighter-shaded area of the circle. The dotted line is the boundary of the original polygon and the solid line is the boundary of the resultant polygon.

If a string parameter is passed to the method, then it will be converted to a float or it will throw an ArgumentException.

A. Calling BufferWithCurves() with a parameter value < 0 on one dimensional geometry instance

The following example returns an empty GeometryCollection instance:

DECLARE @g geometry= 'LINESTRING(3 4, 8 11)';

SELECT @g.BufferWithCurves(-1).ToString();

B. Calling BufferWithCurves() with a parameter value < 0 on a two dimensional geometry instance

The following example returns a CurvePolygon instance with a negative buffer:

DECLARE @g geometry = 'CURVEPOLYGON(COMPOUNDCURVE(CIRCULARSTRING(0 4, 4 0, 8 4), (8 4, 0 4)))';

SELECT @g.BufferWithCurves(-1).ToString()

C. Calling BufferWithCurves() with a parameter value < 0 that returns an empty GeometryCollection

The following example shows what occurs when the distance parameter equals -2:

DECLARE @g geometry = 'CURVEPOLYGON(COMPOUNDCURVE(CIRCULARSTRING(0 4, 4 0, 8 4), (8 4, 0 4)))';

SELECT @g.BufferWithCurves(-2).ToString();

This SELECT statement returns GEOMETRYCOLLECTION EMPTY

D. Calling BufferWithCurves() with a parameter value = 0

The following example returns a copy of the calling geometry instance:

DECLARE @g geometry = 'LINESTRING(3 4, 8 11)';

SELECT @g.BufferWithCurves(0).ToString();

E. Calling BufferWithCurves() with a non-zero parameter value that is extremely small

The following example also returns a copy of the calling geometry instance:

DECLARE @g geometry = 'LINESTRING(3 4, 8 11)';

DECLARE @distance float = 1e-20;

SELECT @g.BufferWithCurves(@distance).ToString();

F. Calling BufferWithCurves() with a parameter value > 0

The following example returns a CurvePolygon instance:

DECLARE @g geometry= 'LINESTRING(3 4, 8 11)';

SELECT @g.BufferWithCurves(2).ToString();

G. Passing a valid string parameter

The following example returns the same CurvePolygon instance as mentioned earlier, but a string parameter is passed to the method:

DECLARE @g geometry= 'LINESTRING(3 4, 8 11)';

SELECT @g.BufferWithCurves('2').ToString();

H. Passing an invalid string parameter

The following example will throw an error:

DECLARE @g geometry = 'LINESTRING(3 4, 8 11)'

SELECT @g.BufferWithCurves('a').ToString();

Note that the previous two examples passed a string literal to the BufferWithCurves() method. The first example works because the string literal can be converted to a numeric value. However, the second example throws an ArgumentException.

I. Calling BufferWithCurves() on MultiPoint instance

The following example returns two GeometryCollection instances and one CurvePolygon instance:

DECLARE @g geometry = 'MULTIPOINT((1 1),(1 4))';

SELECT @g.BufferWithCurves(1).ToString();

SELECT @g.BufferWithCurves(1.5).ToString();

SELECT @g.BufferWithCurves(1.6).ToString();

The first two SELECT statements return a GeometryCollection instance because the parameter distance is less than or equal to 1/2 the distance between the two points (1 1) and (1 4). The third SELECT statement returns a CurvePolygon instance because the buffered instances of the two points (1 1) and (1 4) overlap.

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