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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.

STFilterRings: Removing rings from Polygon based on area.

Monday January 02 2012 at 01:35

Keywordsfunction remove outer inner ring polygon multipolygon geometry area STFilterRings
Summary

A function is presented that allows a user to remove (outer and inner) rings from polygon or multipolygon geometry objects based on area.

A function that have found use in Oracle and PostGIS is one that allows a user to filter out the rings of a polygon or multipolygon based on area.

Here is presented a function to do this in SQL Server Spatial. This function requires Denali (2012) as it uses unionAggregate. In addition, the function requires my Extract function.

  1. USE [GISDB]  -- Change to your database
  2. GO
  3. -- Drop dbo.STFilterRings
  4. --
  5. DROP   FUNCTION dbo.STFilterRings;
  6. -- Create dbo.STFilterRings
  7. --
  8. CREATE FUNCTION dbo.STFilterRings(
  9.   @p_geometry geometry,
  10.   @p_area     FLOAT
  11. )
  12. RETURNS geometry
  13. AS
  14. BEGIN
  15.   DECLARE
  16.      @v_filtered_geom geometry;
  17.   BEGIN
  18.     IF ( @p_geometry IS NULL )
  19.       RETURN NULL;
  20.     IF ( @p_geometry.STGeometryType() NOT IN ('CurvePolygon','Polygon','MultiPolygon') )
  21.     RETURN @p_geometry;
  22.     SELECT @v_filtered_geom = a.outer_rings.STDifference(f.inner_rings)
  23.       FROM (SELECT geometry::UnionAggregate(e.geom) AS outer_rings
  24.               FROM dbo.EXTRACT(@p_geometry,1) AS e
  25.        WHERE e.sid = 1
  26.          AND e.geom.STArea() > @p_area
  27.           ) AS a,
  28.            (SELECT geometry::UnionAggregate(d.geom) AS inner_rings
  29.               FROM (SELECT e.geom
  30.                       FROM dbo.EXTRACT(@p_geometry,1) AS e
  31.                  WHERE e.sid <> 1
  32.                        AND e.geom.STArea() > @p_area
  33.                    ) AS d
  34.            ) f;
  35.     RETURN @v_filtered_geom;
  36.   END;
  37. END
  38. GO

Some tests.

Polygon

  1. -- Original
  2. --
  3. SELECT geometry::STGeomFromText('POLYGON((0 0,20 0,20 20,0 20,0 0),(10 10,10 11,11 11,11 10,10 10),(5 5,5 7,7 7,7 5,5 5))',0) AS geom;

Visually this looks like this.:

  1. -- Rings <= 2sq M removed
  2. --
  3. SELECT dbo.STFilterRings(geometry::STGeomFromText('POLYGON((0 0,20 0,20 20,0 20,0 0),(10 10,10 11,11 11,11 10,10 10),(5 5,5 7,7 7,7 5,5 5))',0),2) AS geom

Visually, this looks like this:

MultiPolygon

  1. -- Original
  2. --
  3. SELECT a.geom.STArea() AS area, a.geom
  4.   FROM (SELECT geometry::STGeomFromText('MULTIPOLYGON (((0 0,20 0,20 20,0 20,0 0),(10 10,10 11,11 11,11 10,10 10),(5 5,5 7,7 7,7 5,5 5)), ((30 30, 50 30, 50 50, 30 50, 30 30)), ((0 30, 20 30, 20 50, 0 50, 0 30)), ((30 0,31 0,31 1,30 1,30 0)))',0) AS geom) AS a;

This looks like this.

area geom
1196 0×0000000001041E0000…..

Visually….

  1. -- Rings <= 2sq M removed
  2. --
  3. SELECT e.geom.STArea() AS area, e.geom
  4.   FROM dbo.EXTRACT(dbo.STFilterRings(geometry::STGeomFromText('MULTIPOLYGON (((0 0,20 0,20 20,0 20,0 0),(10 10,10 11,11 11,11 10,10 10),(5 5,5 7,7 7,7 5,5 5)), ((30 30, 50 30, 50 50, 30 50, 30 30)), ((0 30, 20 30, 20 50, 0 50, 0 30)), ((30 0,31 0,31 1,30 1,30 0)))',0),2.5),1) AS e

This looks like this:

area geom
400 0×0000000001040500…
400 0×0000000001040500…
400 0×0000000001040500…
4 0×0000000001040500…

Visually….

I hope this is useful to someone.

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