LineString
Applies to:
SQL Server
Azure SQL Database
Azure SQL Managed Instance
A LineString is a one-dimensional object representing a sequence of points and the line segments connecting them.
LineString Instances
The illustration below shows examples of LineString instances.
As shown in the illustration:
Figure 1 is a simple, nonclosed LineString instance.
Figure 2 is a nonsimple, nonclosed LineString instance.
Figure 3 is a closed, simple LineString instance, and therefore is a ring.
Figure 4 is a closed, nonsimple LineString instance, and therefore is not a ring.
Accepted Instances
Accepted LineString instances can be input into a geometry variable, but they may not be valid LineString instances. The following criteria must be met for a LineString instance to be accepted. The instance must be formed of at least two points or it must be empty. The following LineString instances are accepted.
DECLARE @g1 geometry = 'LINESTRING EMPTY';
DECLARE @g2 geometry = 'LINESTRING(1 1,2 3,4 8, -6 3)';
DECLARE @g3 geometry = 'LINESTRING(1 1, 1 1)';
@g3
shows that a LineString instance can be accepted, but not valid.
The following LineString instance is not accepted. It will throw a System.FormatException
.
DECLARE @g geometry = 'LINESTRING(1 1)';
Valid Instances
For a LineString instance to be valid, it must meet the following criteria.
- The LineString instance must be accepted.
- If a LineString instance is not empty, then it must contain at least two distinct points.
- The LineString instance cannot overlap itself over an interval of two or more consecutive points.
The following LineString instances are valid.
DECLARE @g1 geometry= 'LINESTRING EMPTY';
DECLARE @g2 geometry= 'LINESTRING(1 1, 3 3)';
DECLARE @g3 geometry= 'LINESTRING(1 1, 3 3, 2 4, 2 0)';
DECLARE @g4 geometry= 'LINESTRING(1 1, 3 3, 2 4, 2 0, 1 1)';
SELECT @g1.STIsValid(), @g2.STIsValid(), @g3.STIsValid(), @g4.STIsValid();
The following LineString instances are not valid.
DECLARE @g1 geometry = 'LINESTRING(1 4, 3 4, 2 4, 2 0)';
DECLARE @g2 geometry = 'LINESTRING(1 1, 1 1)';
SELECT @g1.STIsValid(), @g2.STIsValid();
Warning
The detection of LineString overlaps is based on floating-point calculations, which are not exact.
Examples
Example A.
The following example shows how to create a geometry``LineString
instance with three points and an SRID of 0:
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('LINESTRING(1 1, 2 4, 3 9)', 0);
Example B.
Each point in the LineString
instance may contain Z (elevation) and M (measure) values. This example adds M values to the LineString
instance created in the example above. M and Z can be null values.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('LINESTRING(1 1 NULL 0, 2 4 NULL 12.3, 3 9 NULL 24.5)', 0);
Example C.
The following example shows how to create a geometry LineString
instance with two points that are the same. A call to IsValid
indicates that the LineString instance is not valid and a call to MakeValid
will convert the LineString instance into a Point.
DECLARE @g geometry
SET @g = geometry::STGeomFromText('LINESTRING(1 3, 1 3)',0);
IF @g.STIsValid() = 1
BEGIN
SELECT @g.ToString() + ' is a valid LineString.';
END
ELSE
BEGIN
SELECT @g.ToString() + ' is not a valid LineString.';
SET @g = @g.MakeValid();
SELECT @g.ToString() + ' is a valid Point.';
END
Here is the result set.
LINESTRING(1 3, 1 3) is not a valid LineString
POINT(1 3) is a valid Point.
See Also
STLength (geometry Data Type)
STStartPoint (geometry Data Type)
STEndpoint (geometry Data Type)
STPointN (geometry Data Type)
STNumPoints (geometry Data Type)
STIsRing (geometry Data Type)
STIsClosed (geometry Data Type)
STPointOnSurface (geometry Data Type)
Spatial Data (SQL Server)