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ลงทะเบียนวันนี้CompoundCurve
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
SQL database in Microsoft Fabric
A CompoundCurve is a collection of zero or more continuous CircularString or LineString instances of either geometry or geography types.
An empty CompoundCurve instance can be instantiated, but for a CompoundCurve to be valid it must meet the following criteria:
It must contain at least one CircularString or LineString instance.
The sequence of CircularString or LineString instances must be continuous.
If a CompoundCurve contains a sequence of multiple CircularString and LineString instances, the ending endpoint for every instance except for the last instance must be the starting endpoint for the next instance in the sequence. This means that if the ending point of a prior instance in the sequence is (4 3 7 2), the starting point for the next instance in the sequence must be (4 3 7 2). Z(elevation) and M(measure) values for the point must also be the same. If there is a difference in the two points, a System.FormatException is thrown. Points in a CircularString do not have to have a Z or M value. If no Z or M values are given for the ending point of the prior instance, the starting point of the next instance cannot include Z or M values. If the ending point for the prior sequence is (4 3), the starting point for the next sequence must be (4 3); it cannot be (4 3 7 2). All points in a CompoundCurve instance must have either no Z value or the same Z value.
The following illustration shows valid CompoundCurve types.
CompoundCurve instance is accepted if it is an empty instance or meets the following criteria.
All the instances contained by CompoundCurve instance are accepted circular arc segment instances. For more information on accepted circular arc segment instances, see LineString and CircularString.
All of the circular arc segments in the CompoundCurve instance are connected. The first point for each succeeding circular arc segment is the same as the last point on the preceding circular arc segment.
หมายเหตุ
This includes the Z and M coordinates. So, all four coordinates X, Y, Z, and M must be the same.
None of the contained instances are empty instances.
The following example shows accepted CompoundCurve instances.
SQL
DECLARE @g1 geometry = 'COMPOUNDCURVE EMPTY';
DECLARE @g2 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 0, 0 1, -1 0), (-1 0, 2 0))';
The following example shows CompoundCurve instances that are not accepted. These instances throw System.FormatException.
SQL
DECLARE @g1 geometry = 'COMPOUNDCURVE(CIRCULARSTRING EMPTY)';
DECLARE @g2 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 0, 0 1, -1 0), (1 0, 2 0))';
A CompoundCurve instance is valid if it meets the following criteria.
The CompoundCurve instance is accepted.
All circular arc segment instances contained by the CompoundCurve instance are valid instances.
The following example shows valid CompoundCurve instances.
SQL
DECLARE @g1 geometry = 'COMPOUNDCURVE EMPTY';
DECLARE @g2 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 0, 0 1, -1 0), (-1 0, 2 0))';
DECLARE @g3 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 1, 1 1, 1 1), (1 1, 3 5, 5 4))';
SELECT @g1.STIsValid(), @g2.STIsValid(), @g3.STIsValid();
@g3 is valid because the CircularString instance is valid. For more information on the validity of the CircularString instance, see CircularString.
The following example shows CompoundCurve instances that are not valid.
SQL
DECLARE @g1 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 1, 1 1, 1 1), (1 1, 3 5, 5 4, 3 5))';
DECLARE @g2 geometry = 'COMPOUNDCURVE((1 1, 1 1))';
DECLARE @g3 geometry = 'COMPOUNDCURVE(CIRCULARSTRING(1 1, 2 3, 1 1))';
SELECT @g1.STIsValid(), @g2.STIsValid(), @g3.STIsValid();
@g1 is not valid because the second instance is not a valid LineString instance. @g2 is not valid because the LineString instance is not valid. @g3 is not valid because the CircularString instance is not valid. For more information on valid CircularString and LineString instances, see CircularString and LineString.
The following example shows how to create an empty CompoundCurve instance:
SQL
DECLARE @g geometry;
SET @g = geometry::Parse('COMPOUNDCURVE EMPTY');
The following example shows how to declare and initialize a geometry instance with a CompoundCurvein the same statement:
SQL
DECLARE @g geometry = 'COMPOUNDCURVE ((2 2, 0 0),CIRCULARSTRING (0 0, 1 2.1082, 3 6.3246, 0 7, -3 6.3246, -1 2.1082, 0 0))';
The following example shows how to declare and initialize a geography instance with a CompoundCurve:
SQL
DECLARE @g geography = 'COMPOUNDCURVE(CIRCULARSTRING(-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))';
The following example uses two different ways to use a CompoundCurve instance to store a square.
SQL
DECLARE @g1 geometry, @g2 geometry;
SET @g1 = geometry::Parse('COMPOUNDCURVE((1 1, 1 3), (1 3, 3 3),(3 3, 3 1), (3 1, 1 1))');
SET @g2 = geometry::Parse('COMPOUNDCURVE((1 1, 1 3, 3 3, 3 1, 1 1))');
SELECT @g1.STLength(), @g2.STLength();
The lengths for both @g1 and @g2 are the same. Notice from the example that a CompoundCurve instance can store one or more instances of LineString.
The following example shows how to use two different CircularString instances to initialize a CompoundCurve.
SQL
DECLARE @g geometry;
SET @g = geometry::Parse('COMPOUNDCURVE(CIRCULARSTRING(0 2, 2 0, 4 2), CIRCULARSTRING(4 2, 2 4, 0 2))');
SELECT @g.STLength();
This produces the output 12.5663706143592 which is the equivalent of 4pi. The CompoundCurve instance in the example stores a circle with a radius of 2. Both of the previous code examples did not have to use a CompoundCurve. For the first example a LineString instance would have been simpler, and a CircularString instance would have been simpler for the second example. However, the next example shows where a CompoundCurve provides a better alternative.
The following example uses a CompoundCurve instance to store a semicircle.
SQL
DECLARE @g geometry;
SET @g = geometry::Parse('COMPOUNDCURVE(CIRCULARSTRING(0 2, 2 0, 4 2), (4 2, 0 2))');
SELECT @g.STLength();
The following example shows how multiple CircularString and LineString instances can be stored by using a CompoundCurve.
SQL
DECLARE @g geometry
SET @g = geometry::Parse('COMPOUNDCURVE((3 5, 3 3), CIRCULARSTRING(3 3, 5 1, 7 3), (7 3, 7 5), CIRCULARSTRING(7 5, 5 7, 3 5))');
SELECT @g.STLength();
The following example shows how to use a CompoundCurve instance to store a sequence of CircularString and LineString instances with both Z and M values.
SQL
SET @g = geometry::Parse('COMPOUNDCURVE(CIRCULARSTRING(7 5 4 2, 5 7 4 2, 3 5 4 2), (3 5 4 2, 8 7 4 2))');
The following example shows why CircularString instances must be explicitly declared. The programmer is trying to store a circle in a CompoundCurve instance.
SQL
DECLARE @g1 geometry;
DECLARE @g2 geometry;
SET @g1 = geometry::Parse('COMPOUNDCURVE(CIRCULARSTRING(0 2, 2 0, 4 2), (4 2, 2 4, 0 2))');
SELECT 'Circle One', @g1.STLength() AS Perimeter; -- gives an inaccurate amount
SET @g2 = geometry::Parse('COMPOUNDCURVE(CIRCULARSTRING(0 2, 2 0, 4 2), CIRCULARSTRING(4 2, 2 4, 0 2))');
SELECT 'Circle Two', @g2.STLength() AS Perimeter; -- now we get an accurate amount
Here's the result set.
เอาท์พุท
Circle One11.940039...
Circle Two12.566370...
The perimeter for Circle Two is approximately 4pi, which is the actual value for the perimeter. However, the perimeter for Circle One is significantly inaccurate. Circle One's CompoundCurve instance stores one circular arc segment (ABC) and two line segments (CD, DA). The CompoundCurve instance has to store two circular arc segments (ABC, CDA) to define a circle. A LineString instance defines the second set of points (4 2, 2 4, 0 2) in Circle One's CompoundCurve instance. You have to explicitly declare a CircularString instance inside a CompoundCurve.