CurveToLineWithTolerance (geometry Data Type)

Article
02/28/2023

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

Returns a polygonal approximation of a geometry instance that contains circular arc segments.

Syntax

  
.CurveToLineWithTolerance ( tolerance, relative )

Arguments

tolerance
Is a double expression that defines the maximum error between the original circular arc segment and its linear approximation.

relative
Is a bool expression that indicates whether to use a relative maximum for the deviation. When relative is set to false (0), then an absolute maximum is set for the deviation that a linear approximate can have. When relative is set to true (1) then the tolerance is calculated as a product of the tolerance parameter and the diameter of the bounding box for the spatial object.

Return Types

SQL Server return type: geometry

CLR return type: SqlGeometry

Exceptions

Setting tolerance <= 0 throws an ArgumentOutOfRange exception.

Remarks

This method can specify an error tolerance amount for the resultant LineString.

The following table shows the instance type returned by CurveToLineWithTolerance()for various types.

Invoking Instance Type	Spatial Type Returned
Empty geometry instance	Empty GeometryCollection instance
Point and MultiPoint	Point instance
MultiPoint	Point or MultiPoint instance
CircularString, CompoundCurve, or LineString	LineString instance
MultiLineString	LineString or MultiLineString instance
CurvePolygon and Polygon	Polygon instance
MultiPolygon	Polygon or MultiPolygon instance
GeometryCollection with a single instance that does not contain a circular arc segment	The instance that is contained in the GeometryCollection determines the type of instance returned.
GeometryCollection with a single one-dimensional circular arc segment instance (CircularString, CompoundCurve)	LineString instance
GeometryCollection with a single two-dimensional circular arc segment instance (CurvePolygon)	Polygon instance
GeometryCollection with multiple one dimensional instances	MultiLineString instance
GeometryCollection with multiple two dimensional instances	MultiPolygon instance
GeometryCollection with multiple instances of different dimensions	GeometryCollection instance

Examples

A. Using different tolerance values on a CircularString instance

The following example shows how setting the tolerance affects the LineStringinstance returned from a CircularString instance:

 DECLARE @g geometry; 
 SET @g = geometry::Parse('CIRCULARSTRING(0 0, 1 2.1082, 3 6.3246, 0 7, -3 6.3246, -1 2.1082, 0 0)'); 
 SELECT @g.CurveToLineWithTolerance(0.1,0).STNumPoints(), @g.CurveToLineWithTolerance(0.01, 0).STNumPoints();

B. Using the method on a MultiLineString instance containing one LineString

The following example shows what is returned from a MultiLineString instance that only contains one LineString instance:

 DECLARE @g geometry; 
 SET @g = geometry::Parse('MULTILINESTRING((1 3, 4 8, 6 9))'); 
 SELECT @g.CurveToLineWithTolerance(0.1,0).ToString();

C. Using the method on a MultiLineString instance containing multiple LineStrings

The following example shows what is returned from a MultiLineString instance that contains more than one LineString instance:

 DECLARE @g geometry; 
 SET @g = geometry::Parse('MULTILINESTRING((1 3, 4 8, 6 9),(4 4, 9 18))'); 
 SELECT @g.CurveToLineWithTolerance(0.1,0).ToString();

D. Setting relative to true for an invoking CurvePolygon instance

The following example uses a CurvePolygon instance to call CurveToLineWithTolerance() with relative set to true:

 DECLARE @g geometry = 'CURVEPOLYGON(COMPOUNDCURVE(CIRCULARSTRING(0 4, 4 0, 8 4), (8 4, 0 4)))'; 
 SELECT @g.CurveToLineWithTolerance(.5,1).ToString();

E. Using the method on a GeometryCollection instance

The following example calls CurveToLineWithTolerance() on a GeometryCollection that contains a two-dimensional CurvePolygon instance and a one-dimensional CircularString instance. CurveToLineWithTolerance() converts both circular arc segment types to line segment types and returns them in a GeometryCollection type.

 DECLARE @g geometry; 
 SET @g = geometry::Parse('GEOMETRYCOLLECTION(CURVEPOLYGON( COMPOUNDCURVE(CIRCULARSTRING(0 2, 2 0, 4 2), (4 2, 0 2))), CIRCULARSTRING(4 4, 8 6, 9 5))'); 
 SELECT @g.CurveToLineWithTolerance(0.1,0).STNumPoints(), @g.CurveToLineWithTolerance(0.1, 0).ToString();

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