BufferWithTolerance (geometry Data Type)

Artikel
11/19/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance SQL database in Microsoft Fabric

Returns a geometric object that represents the union of all point values whose distance from a geometry instance is less than or equal to a specified value, allowing for a specified tolerance.

Syntax

  
.BufferWithTolerance ( distance, tolerance, relative )

Arguments

distance
Is a float expression specifying the distance from the geometry instance around which to calculate the buffer.

tolerance
Is a float expression specifying the tolerance of the buffer distance.

Tolerance refers to the maximum variation in the ideal buffer distance for the returned linear approximation.

For example, the ideal buffer distance of a point is a circle, but this must be approximated by a polygon. The smaller the tolerance, the more points the polygon will have, which increases the complexity of the result, but decreases the error.

relative
Is a bit specifying whether the tolerance value is relative or absolute. If 'TRUE' or 1, then tolerance is relative and is calculated as the product of the tolerance parameter and the diameter of the bounding box of the instance. If 'FALSE' or 0, tolerance is absolute and the tolerance value is the absolute maximum variation in the ideal buffer distance for the returned linear approximation.

Return Types

SQL Server return type: geometry

CLR return type: SqlGeometry

Exceptions

The tolerance parameter must be greater than zero. If tolerance <= 0 then a System.ArgumentOutOfRangeException is thrown.

Note

Since tolerance is a float type, a System.Runtime.InteropServices.COMException can be thrown if the value given for tolerance is very small because of the rounding issues with floating point types.

Remarks

When distance > 0 then either a Polygon or MultiPolygon instance is returned.

Note

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

When distance = 0 then a copy of the calling geometry instance is returned.

When distance < 0 then

An empty GeometryCollection instance is returned when the dimensions of the instance are 0 or 1.
A negative buffer is returned when the dimensions of the instance are 2 or more.

Note

A negative buffer may also create an empty GeometryCollection instance.

A negative buffer removes all points within the given distance of the boundary of the geometry instance.

The error between the theoretical and computed buffer is max(tolerance, extents * 1.E-7) where tolerance is the value of the tolerance parameter. For more information on extents, see geometry Data Type Method Reference.

Examples

The following example creates a Point instance and uses BufferWithTolerance() to obtain a rough buffer around it.

DECLARE @g geometry;  
SET @g = geometry::STGeomFromText('POINT(3 3)', 0);  
SELECT @g.BufferWithTolerance(1, .5, 0).ToString();

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