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    STGeometryTypes: Extracting all geometry type string values from complex geometry
    STDensify: Densify (m)LineString or (m)Polygon geometry objects
    STInsertN: Insert single vertex into a geometry
    STUpdateN: Update (replace) a single vertex within a geometry object.
    STUpdate: Replace all points equal to the supplied point with replacement point.
    STDeleteN: Delete single vertex from geometry
    STDelete: Deleting vertices in geometry objects
    STFlipVectors: Normalize direction of linestring vectors
    STConvertToLineString: Extract LineStrings in GeometryCollection to create LineString
    STLine2Cogo: Converting LineStrings to COGO XML
    STCogo2Line: Creating (Multi)LineStrings geometries from COGO XML instructions
    STVectorize: Break Linestring/Polygon elements into 2 point vectors (or 3 point circular curves)
    STScale: Function to Scale a geometry object
    TSQL String Tokenizer Function for SQL Server
    STGeometry2MBR/STGeography2MBR: Compute and return MBR ordinates
    generate_series for SQL Server 2008
    STExtractPolygon: Extract Polygons from result of STIntersection in SQL Server Spatial
    STRound: Function to round ordinates of a SQL Server Spatial geometry object
    STExtract: Extract elements of a geometry object
    STNumRings: Counting number of polygon rings
    STFilterRings: Removing rings from Polygon based on area.
    STMove: Function to Move a geometry object in SQL Server Spatial
    STCentroid*: Alternate Functions for Compute a Centroid
    STRotate: Function to rotate a geometry object in SQL Server Spatial
    STVertices: Wrapper over STDumpPoints
    STMorton: Creating a Morton number Space Key value for grid square
    Gridding a geometry or geography object (SQL Server Denali)
    On hinting spatial indexes
    RandomSearchByExtent: Random Search Procedure (2008 Spatial)
    COGO: Convert DMS String to decimal degrees floating point number.
    COGO: Converting (Google Earth) Formatted Longitude/Latitude points to decimal degrees (SQL Server)
    COGO: Convert Degrees, Minutes and Seconds values to Decimal Degrees
    COGO: DD2DMS Formatting a latitude/longitude decimal degree value
    COGO: Create point from bearing and distance
    COGO: Compute number of vertices required to stroke circle or circular arc
    COGO: Calculating the bearing between two points (SQL Server 2008 Spatial)
    COGO: Compute arc length subtended by angle centre of circle
    COGO: Compute chord length of segment of a circle (arc)
    COGO: Computing Arc To Chord (Arc2Chord) Separation
    COGO: Creating a stroked polygon from a circle's centre x,y and radius
    COGO: Finding centre and radius of a curve defined by three points: FindCircle function
    CheckRadii: Identifying Tight Radius Curves sections within LineString geometry data
    Generating random point data for SQL Server 2008 Spatial
    New Presentation on Active (Searchable) Spatial Metadata for SQL Server 2008 Spatial and FreeText
    STisGeo: Checking if a column in a table or a view is of type geometry or geography
    Vectorising geometry objects in SQL Server 2008
    STMBR2Geometry/STMBR2Geography functions
    Extracting geometry types from geometry/geography objects in SQL Server 2008
    Getting the number of coordinate dimensions of a geometry/geography object in SQL Server 2008
    STDumpPoints: A Function that Dumps the Vertices/Points in a geometry
    toGeography and toGeography Conversion Functions for SQL Server 2008 Spatial
    Write text file with spatial data from SQL Server 2008
    Loading Shapefiles into Geography type column in SQL Server 2008
    Tip #6: Correcting invalid geometries
    Tip #5: Where or where has my little column gone
    Tip #4: What Coordinate System is that?
    Tip #3: What object is that?
    Tip #2: Spatial Indexing and Primary Keys
    Tip #1: SQL Server 2008 "Katmai" - Setting SRIDs

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All Blog Articles, Data Models and Free Source Code by Simon Greener, The SpatialDB Advisor is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Getting the number of coordinate dimensions of a geometry/geography object in SQL Server 2008

Monday September 28 2009 at 07:47

The OGC standard has an STDimension() method defined on geometry/geography objects and this is implemented in SQL Server 2009. This function returns the inherent (or topological) dimensionality of an object: for a point this is 0; for a linestring this is 1; and for a polygon this is 2.

SELECT [name], [geom].STDimension() as [dim]
  FROM (  select 'Point' as name, geometry::STGeomFromText('POINT(3 3)', 0) as geom
union all select 'LineString' as name, geometry::STGeomFromText('LINESTRING(0 0, 3 3)', 0) as geom
union all select 'Polygon' as name, geometry::STGeomFromText('POLYGON((0 0, 3 0, 0 3, 0 0))', 0) as geom) as a;

name dim
Point 0
LineString 1
Polygon 2



But what if you wanted to know the coordinate dimensionality of an object? That is whether an object is:

  • 2D ie has only X,Y ordinates; or
  • 3D ie has X,Y and Z ordinates defined; or
  • 4D ie has X,Y,Z and M ordinates defined?

The OGC standard cannot help here and no such function has been implemented in SQL Server.

Now, in Oracle, a method called GET_DIMS() is defined on the sdo_geometry object that returns the coordinate dimensionality of an object and, in PostGIS, a function called ST_NDims() is defined. What can we do for SQL Server 2008 Spatial?

Here is a function called NDims that implements what we are after.

USE [GISDB]  -- Change to your database
GO

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

Create Function [dbo].[NDims]( @p_geom geometry )
  Returns Int
As
BEGIN
    Declare
      @v_ndims Int;
    Begin
        SELECT @v_ndims = ( 2 + 
                          case when c.point.Z IS NULL then 0 else 1 end + 
                          case when c.point.M IS NULL then 0 else 1 end )
          FROM (SELECT geometry::STGeomFromText(b.PointText,0) as point
                  FROM (select Top 1
                               case when geom.STGeometryType() = 'Point'           then geom.AsTextZM()
                                    when geom.STGeometryType() = 'MultiPoint'      then geom.STGeometryN(1).AsTextZM()
                                    when geom.STGeometryType() = 'LineString'      then geom.STPointN(1).AsTextZM()
                                    when geom.STGeometryType() = 'MultiLineString' then geom.STGeometryN(1).STPointN(1).AsTextZM()
                                    when geom.STGeometryType() = 'Polygon'         then geom.STExteriorRing().STPointN(1).AsTextZM()
                                    when geom.STGeometryType() = 'MultiPolygon'    then geom.STGeometryN(1).STExteriorRing().STPointN(1).AsTextZM()
                                 end as pointText
                          from (select case when @p_geom.STGeometryType() = 'GeometryCollection' 
                                            then @p_geom.STGeometryN(1) 
                                            else @p_geom 
                                         end as geom ) as a
                ) as b
          ) as c;
         RETURN @v_ndims;
    END;
END
GO

Note that the function is defined only on the geometry object type. The function can be called for geography object types via the use of my toGeometry/toGeography functions.

Testing

Testing this function with a variety of data returns the following:

          select dbo.ndims(geometry::STGeomFromText('POINT(0 1)',0)) as pDim
union all select dbo.ndims(geometry::STGeomFromText('POINT(0 1 2)',0)) as pDim
union all select dbo.ndims(geometry::STGeomFromText('POINT(0 1 2 3)',0)) as pDim;

pDim
2
3
4

select dbo.ndims(geometry::STGeomFromText('MULTIPOINT((0 0 0), (1 1 1), (2 2 2), (3 3 3))',0)) as mpDim;

mpDim
3

          select dbo.ndims(geometry::STGeomFromText('LINESTRING(0 0, 1 1)',0)) as lDim
union all select dbo.ndims(geometry::STGeomFromText('LINESTRING(0 0 0, 1 1 1, 2 2 2, 3 3 3)',0)) as lDim
union all select dbo.ndims(geometry::STGeomFromText('LINESTRING(0 0 0 0, 1 1 1 1, 2 2 2 2, 3 3 3 3)',0)) as lDim;

lDim
2
3
4

          select dbo.ndims(geometry::STGeomFromText('MULTILINESTRING((0 0,1 1,1 2),(2 3,3 2,5 4))',0)) as mlDim
union all select dbo.ndims(geometry::STGeomFromText('MULTILINESTRING((0 0 0,1 1 1,2 2 2),(3 3 3,4 4 4,5 5 5))',0)) as mlDim
union all select dbo.ndims(geometry::STGeomFromText('MULTILINESTRING((0 0 0 0,1 1 1 1,2 2 2 2),(3 3 3 3,4 4 4 4,5 5 5 5))',0)) as mlDim;

mlDim
2
3
4

          select dbo.ndims(geometry::STGeomFromText('POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))',0)) as dPoly
union all select dbo.ndims(geometry::STGeomFromText('POLYGON ((0 0 0, 1 0 0, 1 1 0, 0 1 0, 0 0 0))',0)) as dPoly;

dPoly
2
3

          select dbo.ndims(geometry::STGeomFromText('MULTIPOLYGON (((20 20, 40 20, 40 40, 20 40, 20 20)), ((0 0, 10 0, 10 10, 0 10, 0 0), (4 4, 4 6, 6 6, 6 4, 4 4)))',0)) as dMPoly
union all select dbo.ndims(geometry::STGeomFromText('MULTIPOLYGON (((20 20 0, 40 20 0, 40 40 0, 20 40 0, 20 20 0)), ((0 0 0, 10 0 0, 10 10 0, 0 10 0, 0 0 0), (4 4 0, 4 6 0, 6 6 0, 6 4 0, 4 4 0)))',0)) as dMPoly;

dMPoly
2
3

select dbo.ndims(geometry::STGeomFromText('GEOMETRYCOLLECTION(POINT(2 3 4),LINESTRING(2 3 4,3 4 5),POLYGON ((0 0 0, 1 0 0, 1 1 0, 0 1 0, 0 0 0)))',0)) as dGC;

dGC
3



Geography

If we have a geography object we can still find its coordinate dimensionality via use of the toGeometry/toGeography functions.

select dbo.NDims(
         dbo.toGeometry(geography::STGeomFromText('POLYGON ((148.0 -44.0, 148.0 -43.0, 147.0 -43.0, 147.0 -44.0, 148.0 -44.0), (147.4 -43.6, 147.2 -43.6, 147.2 -43.2, 147.4 -43.2, 147.4 -43.6))',4326),
                        0)) as dGeogPoly;

dGeogPoly
2



I hope this function is useful to somebody.

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Comment [1]

Thank you, this function was very useful to me, since I wanted to find all geometries that are not 3-dimensional. It’s strange to me that function STDimension() is used for getting the type of geometry, when by the name of it you would think it get you dimension (2D, 3D…).

13 July 2016, 20:33 #