BufferWithCurves (geography Data Type)

Article
02/28/2023

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

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

Syntax

  
.BufferWithCurves ( distance )

Arguments

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

Return Types

SQL Server return type: geography

CLR return type: SqlGeography

Exceptions

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)

Remarks

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: A negative buffer may create an empty GeometryCollection
distance = 0	All dimensions	Copy of the invoking geography instance
distance > 0	All dimensions	CurvePolygon or GeometryCollection instance

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 geography instance is returned.

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

Examples

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

The following example returns an empty GeometryCollection instance:

DECLARE @g geography= 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)';  
SELECT @g.BufferWithCurves(-1).ToString();

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

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

DECLARE @g geography = 'CURVEPOLYGON(CIRCULARSTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))';  
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 geography = 'CURVEPOLYGON(CIRCULARSTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))';  
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 geography instance:

DECLARE @g geography = 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)';  
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 geography instance:

DECLARE @g geography = 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)';  
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 geography= 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)';  
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 geography= 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)';  
SELECT @g.BufferWithCurves('2').ToString();

H. Passing an invalid string parameter

The following example will throw an error:

DECLARE @g geography = 'LINESTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653)'  
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.

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