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Create, Construct, and Query geometry Instances

The planar spatial data type, geometry, represents data in a Euclidean (flat) coordinate system. This type is implemented as a common language runtime (CLR) data type in SQL Server.

The geometry type is predefined and available in each database. You can create table columns of type geometry and operate on geometry data in the same manner as you would use other CLR types.

The geometry data type (planar) supported by SQL Server conforms to the Open Geospatial Consortium (OGC) Simple Features for SQL Specification version 1.1.0.

For more information on OGC specifications, see the following:

SQL Server supports a subset of the existing GML 3.1 standard which is defined in the following schema: http://schemas.microsoft.com/sqlserver/profiles/gml/SpatialGML.xsd.

Creating a New geometry Instance from an Existing Instance

The geometry data type provides numerous built-in methods you can use to create new geometry instances based on existing instances.

To create a buffer around a geometry

STBuffer (geometry Data Type)

BufferWithTolerance (geometry Data Type)

To create a simplified version of a geometry

Reduce (geometry Data Type)

To create the convex hull of a geometry

STConvexHull (geometry Data Type)

To create a geometry from the intersection of two geometries

STIntersection (geometry Data Type)

To create a geometry from the union of two geometries

STUnion (geometry Data Type)

To create a geometry from the points where one geometry does not overlap another

STDifference (geometry Data Type)

To create a geometry from the points where two geometries do not overlap

STSymDifference (geometry Data Type)

To create an arbitrary Point instance that lies on an existing geometry

STPointOnSurface (geometry Data Type)

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Constructing a geometry Instance from Well-Known Text Input

The geometry data type provides several built-in methods that generate a geometry from the Open Geospatial Consortium (OGC) WKT representation. The WKT standard is a text string that allows geometry data to be exchanged in textual form.

To construct any type of geometry instance from WKT input

STGeomFromText (geometry Data Type)

Parse (geometry Data Type)

To construct a geometry Point instance from WKT input

STPointFromText (geometry Data Type)

To construct a geometry MultiPoint instance from WKT input

STMPointFromText (geometry Data Type)

To construct a geometry LineString instance from WKT input

STLineFromText (geometry Data Type)

To construct a geometry MultiLineString instance from WKT input

STMLineFromText (geometry Data Type)

To construct a geometry Polygon instance from WKT input

STPolyFromText (geometry Data Type)

To construct a geometry MultiPolygon instance from WKT input

STMPolyFromText (geometry Data Type)

To construct a geometry GeometryCollection instance from WKT input

STGeomCollFromText (geometry Data Type)

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Constructing a geometry Instance from Well-Known Binary Input

WKB is a binary format specified by the Open Geospatial Consortium (OGC) that permits geometry data to be exchanged between a client application and an SQL database. The following functions accept WKB input to construct geometries:

To construct any type of geometry instance from WKB input

STGeomFromWKB (geometry Data Type)

To construct a geometry Point instance from WKB input

STPointFromWKB (geometry Data Type)

To construct a geometry MultiPoint instance from WKB input

STMPointFromWKB (geometry Data Type)

To construct a geometry LineString instance from WKB input

STLineFromWKB (geometry Data Type)

To construct a geometry MultiLineString instance from WKB input

STMLineFromWKB (geometry Data Type)

To construct a geometry Polygon instance from WKB input

STPolyFromWKB (geometry Data Type)

To construct a geometry MultiPolygon instance from WKB input

STMPolyFromWKB (geometry Data Type)

To construct a geometry GeometryCollection instance from WKB input

STGeomCollFromWKB (geometry Data Type)

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Constructing a geometry Instance from GML Text Input

The geometry data type provides a method that generates a geometry instance from GML, an XML representation of geometric objects. SQL Server supports a subset of GML.

To construct any type of geometry instance from GML input

GeomFromGml (geometry Data Type)

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You can use the following methods to return either the WKT or WKB format of a geometry instance:

To return the WKT representation of a geometry instance

STAsText (geometry Data Type)

ToString (geometry Data Type)

To return the WKT representation of a geometry instance including any Z and M values

AsTextZM (geometry Data Type)

To return the WKB representation of a geometry instance

STAsBinary (geometry Data Type)

To return a GML representation of a geometry instance

AsGml (geometry Data Type)

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All geometry instances have a number of properties that can be retrieved through methods that SQL Server provides. The following topics define the properties and behaviors of geometry types, and the methods for querying each one.

Validity, Instance Type, and GeometryCollection Information

Once a geometry instance is constructed, you can use the following methods to determine if it is well-formed, return the instance type, or, if it is a collection instance, return a specific geometry instance.

To return the instance type of a geometry

STGeometryType (geometry Data Type)

To determine if a geometry is a given instance type

InstanceOf (geometry Data Type)

To determine if a geometry instance is well-formed for its instance type

STIsValid (geometry Data Type)

To convert a geometry instance to a well-formed geometry instance with an instance type

MakeValid (geometry Data Type)

To return the number of geometries in a geometry collection instance

STNumGeometries (geometry Data Type)

To return a specific geometry in a geometry collection instance

STGeometryN (geometry Data Type) STGeometryN (geometry Data type)

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Number of Points

All nonempty geometry instances are comprised of points. These points represent the X- and Y-coordinates of the plane on which the geometries are drawn. geometry provides numerous built-in methods for querying the points of an instance.

To return the number of points that comprise an instance

STNumPoints (geometry Data Type)

To return a specific point in an instance

STPointN

To return an arbitrary point that lies on an instance

STPointOnSurface

To return the start point of an instance

STStartPoint

To return the end point of an instance

STEndpoint

To return the X-coordinate of a Point instance

STX (geometry Data Type)

To return the Y-coordinate of a Point instance

STY

To return the geometric center point of a Polygon, CurvePolygon, or MultiPolygon instance

STCentroid

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Dimension

A nonempty geometry instance can be 0-, 1-, or 2-dimensional. Zero-dimensional geometries, such as Point and MultiPoint, have no length or area. One-dimensional objects, such as LineString, CircularString, CompoundCurve, and MultiLineString, have length. Two-dimensional instances, such as Polygon, CurvePolygon, and MultiPolygon, have area and length. Empty instances will report a dimension of -1, and a GeometryCollection will report an area dependent on the types of its contents.

To return the dimension of an instance

STDimension

To return the length of an instance

STLength

To return the area of an instance

STArea

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Empty

An empty geometry instance does not have any points. The length of empty LineString, CircularString, CompoundCurve, and MultiLineString instances is zero. The area of empty Polygon, CurvePolygon, and MultiPolygon instances is 0.

To determine if an instance is empty

STIsEmpty.

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Simple

For a geometry of the instance to be simple, it must meet both of these requirements:

  • Each figure of the instance must not intersect itself, except at its endpoints.

  • No two figures of the instance can intersect each other at a point that is not in both of their boundaries.

Note Note

Empty geometries are always simple.

To determine if an instance is simple

STIsSimple.

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Boundary, Interior, and Exterior

The interior of a geometry instance is the space occupied by the instance, and the exterior is the space not occupied it.

Boundary is defined by the OGC as follows:

  • Point and MultiPoint instances do not have a boundary.

  • LineString and MultiLineString boundaries are formed by the start points and end points, removing those that occur an even number of times.

DECLARE @g geometry;
SET @g = geometry::Parse('MULTILINESTRING((0 1, 0 0, 1 0, 0 1), (1 1, 1 0))');
SELECT @g.STBoundary().ToString();

The boundary of a Polygon or MultiPolygon instance is the set of its rings.

DECLARE @g geometry;
SET @g = geometry::Parse('POLYGON((0 0, 3 0, 3 3, 0 3, 0 0), (1 1, 1 2, 2 2, 2 1, 1 1))');
SELECT @g.STBoundary().ToString();
To return the boundary of an instance

STBoundary

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Envelope

The envelope of a geometry instance, also known as the bounding box, is the axis-aligned rectangle formed by the minimum and maximum (X,Y) coordinates of the instance.

To return the envelope of an instance

STEnvelope

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Closure

A closed geometry instance is a figure whose start points and end points are the same. Polygon instances are considered closed. Point instances are not closed.

A ring is a simple, closed LineString instance.

To determine if an instance is closed

STIsClosed

To determine if an instance is a ring

STIsRing

To return the exterior ring of a Polygon instance

STExteriorRing

To return the number of interior rings in a Polygon

STNumInteriorRing

To return a specified interior ring of a Polygon

STInteriorRingN

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Spatial Reference ID (SRID)

The spatial reference ID (SRID) is an identifier specifying which coordinate system the geometry instance is represented in. Two instances with different SRIDs are incomparable.

To set or return the SRID of an instance

STSrid

This property can be modified.

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The geometry data type provides many built-in methods you can use to determine relationships between two geometry instances.

To determine if two instances comprise the same point set

STEquals

To determine if two instances are disjoint

STDisjoint

To determine if two instances intersect

STIntersects

To determine if two instances touch

STTouches

To determine if two instances overlap

STOverlaps

To determine if two instances cross

STCrosses

To determine if one instance is within another

STWithin

To determine if one instance contains another

STContains

To determine if one instance overlaps another

STOverlaps

To determine if two instances are spatially related

STRelate

To determine the shortest distance between points in two geometries

STDistance

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The default SRID for geometry instances in SQL Server is 0. With geometry spatial data, the specific SRID of the spatial instance is not required to perform calculations; thus, instances can reside in undefined planar space. To indicate undefined planar space in the calculations of geometry data type methods, the SQL Server Database Engine uses SRID 0.

The following two examples show how to add and query geometry data.

  • The first example creates a table with an identity column and a geometry column GeomCol1. A third column renders the geometry column into its Open Geospatial Consortium (OGC) Well-Known Text (WKT) representation, and uses the STAsText() method. Two rows are then inserted: one row contains a LineString instance of geometry, and one row contains a Polygon instance.

    IF OBJECT_ID ( 'dbo.SpatialTable', 'U' ) IS NOT NULL 
        DROP TABLE dbo.SpatialTable;
    GO
    
    CREATE TABLE SpatialTable 
        ( id int IDENTITY (1,1),
        GeomCol1 geometry, 
        GeomCol2 AS GeomCol1.STAsText() );
    GO
    
    INSERT INTO SpatialTable (GeomCol1)
    VALUES (geometry::STGeomFromText('LINESTRING (100 100, 20 180, 180 180)', 0));
    
    INSERT INTO SpatialTable (GeomCol1)
    VALUES (geometry::STGeomFromText('POLYGON ((0 0, 150 0, 150 150, 0 150, 0 0))', 0));
    GO
    
  • The second example uses the STIntersection() method to return the points where the two previously inserted geometry instances intersect.

    DECLARE @geom1 geometry;
    DECLARE @geom2 geometry;
    DECLARE @result geometry;
    
    SELECT @geom1 = GeomCol1 FROM SpatialTable WHERE id = 1;
    SELECT @geom2 = GeomCol1 FROM SpatialTable WHERE id = 2;
    SELECT @result = @geom1.STIntersection(@geom2);
    SELECT @result.STAsText();
    

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