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.
Syntax
.BufferWithCurves ( distance )
Arguments
- distance
Is a float indicating the maximum distance that points forming the buffer can be from the geometry instance.
Return Types
SQL Server return type: geometry
CLR return type: SqlGeometry
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 illustration shows an example of a geometry instance returned by this method.
.gif "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 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
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.
Examples
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.