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Current Oracle Spatial Blog Articles

    Convert Single Geometry to Multi-part Geometry in Oracle Spatial
    Optimized Rectangle to 5 Point Polygon
    Centroid Package now supports Y ordinate seeding
    Convert GeoJSON document to Sdo_Geometry objects
    Implementation Of Travelling Salesman Problem
    Create Polygon From Bearings And Distances
    Function That Returns a Compass Point From a Whole Circle Bearing
    Playing around with Centroids by using different seed values
    GeoRaptor 4.x Update 2
    Simple Oracle C Sprintf or Java String.format
    Some Oriented Point Functions
    Extracting Inner Rings Changed Ordinate Ordering: A Trap For Players Who Don't Read Documentation!
    PLS-00306: wrong number or types of arguments in call to 'SDO_GEOMETRY'
    Converting Google Earth Formatted Longitude/Latitude points to decimal degrees
    Oracle Business Intelligence Warehousing and Analytics - Spatial Summit
    How far inside, is inside? Measuring actual distance.
    Noding and building a polygon from single, overlapping linestrings
    Analyzing Spatial Query Performance Improvements in Oracle Spatial and Graph 12c Through Cross-Vendor Comparison
    ST_VertexN / ST_PointN - Extracting a specific point from any geometry
    Convert Single Point stored in SDO_ORDINATES to SDO_POINT_TYPE
    Aggregate APPEND Islands and XOR polygons
    Circular Arcs in Geodetic Polygons
    Some SDO_GEOMETRY/DIMINFO handling functions
    Applying And Extending Oracle Spatial - Book Released
    Changing all DIMINFO sdo_tolerance values for all metadata records in one go.
    Building Polygons from Incomplete Linestrings using ST_PolygonBuilder
    Computing Cardinal Directions to nearby geometries
    Intersecting two aggregated polygon layers with SC4O
    Spatial and Oracle 12c
    Update Triggers and SDO_GEOMETRY Equality
    Duplicate Geometry data and Data Models
    CENTROID package update
    How to calculate cumulative length of a linestring
    Useful Package of Wrapper Functions for Sdo_Util.AffineTransforms
    Compute Location from known Lat/Long point using delta easting and northing in miles
    Sorting SDO_GEOMETRY data using the ORDER BY clause of a SELECT statement
    Creating linestrings from points
    Rounding Coordinates or Ordinates in SDO_GEOMETRY
    Effects of Sdo_Geometry Ordinate Precision on Performance
    Effects of Sdo_Geometry Ordinate Precision on Storage
    The Spatial filtering of geometries: The effect of tolerances on relationships
    Application of Delaunay Triangulation and Inverse Distance Weighting (IDW) in Oracle for Soils Interpolation
    Selecting all SDO_GTYPE values for all tables/sdo_geometry columns in a schema
    CENTROID package - Tips for Use
    Announcing the Spatial Companion For Oracle (SC4O)
    Filtering Rings (Oracle Spatial)
    Splitting a polygon using one or more linestrings
    isValid, isSimple, Dimension and CoordDim methods for SDO_Geometry
    Line Merging or Collecting lines together: ST_LineMerger
    ST_DeleteVertex for Oracle SDO_Geometry based on Jaspa/JTS
    3D/4D and SRID aware Conversion functions for SDO_Geometry: WKT and EWKT
    Topological vs Non-Topological Simplification/Generalization of Aggregated Area Geometies in Oracle
    Filtering very short linestrings via bitmap function index
    CENTROID For Oracle
    Gridding a sdo_geometry line/polygon object (Oracle)
    Finding centre and radius of a circular geometry
    Constraining geometry type for sdo_geometry column in a table.
    CASE Statements and SDO_GEOMETRY
    The Power of Constraints and Indexes for Spatial Constraints: stopping duplicate points
    Replacement for SDO_GEOM.RELATE - ST_Relate based on JTS
    Changing Oracle Spatial Index Parameters on existing index
    Writing Excel Spreadsheets files from within the Oracle database using Java and PL/SQL
    Writing xSV (eg csv) files from within the Oracle database using Java and PL/SQL
    A simple spike finder for Spatial/Locator
    JTS Java class compilation for 11g and above
    Random Spatial Search Procedure
    Geometry Snapping using JTS in Oracle
    Exposing JTS's MinimumBoundingCircle functionality
    Exposing JTS's Densifier functionality
    Using JTS's Comparison Functions - HausdorffSimilarityMeasure & AreaSimilarityMeasure with SDO_GEOMETRY
    Free JTS-based Area/Length Functions
    Handy way of systematically fixing polygon geometries with 13349 and other errors
    Standalone CENTROID package now available for download
    Free Union, Intersection, Xor and Difference Functions for Oracle Locator - Part 4 Processing Geodetic data
    Configurable Buffer: JTS and Oracle
    Free Union, Intersection, Xor and Difference Functions for Oracle Locator - Part 3
    Free Union, Intersection, Xor and Difference Functions for Oracle Locator - Part 2
    Free Union, Intersection, Xor and Difference Functions for Oracle Locator - Part 1
    Building Lines into Polygons in Oracle Locator / Spatial
    Finding Intersection Points between Line and Polygon
    Free version of sdo_length
    Alternative to my SQL based GetNumRings function
    External Tables and SDO_Geometry data.
    layer_gtype keyword issue when indexing linear data on 11g
    String Tokenizer for Oracle
    Free Aggregate Method for Concatenating 2D Lines in Oracle Locator 10g
    Reducing 5 Vertex Polygon to Optimized Rectangle
    Square Buffer
    Converting decimal seconds to string
    Valid conversion unit values for Oracle sdo_geom.sdo_length()
    Removing Steps in Gridded Vector Data - SmoothGrid for Oracle
    Oracle Spatial DISJOINT search/filtering
    Creating SDO_Geometry from geometric data recorded in the columns of a table
    Concave Hull Geometries in Oracle 11gR2
    Projecting SDO_GEOM_METADATA DIMINFO XY ordinates
    Instantiating MDSYS.VERTEX_TYPE
    New PL/SQL Packages - Rotate oriented point
    GeoRaptor Development Team
    Fast Refreshing Materialized View Containing SDO_GEOMETRY and SDO_GEOM.SDO_AREA function
    Performance of PL/SQL Functions using SQL vs Pure Code
    Implementing the BEST VicGrid Projection in Oracle 10gR2
    Making Sdo Geometry Metadata Update Generic Code
    ORA-13011 errors when using SDO_GEOM.VALIDATE_LAYER_WITH_CONTEXT()
    Extract Polygons from Compound Polygon
    Detecting sdo_geometries with compound (3-point Arcs) segments
    GEOMETRY_COLUMNS for Oracle Spatial
    Convert GML to SDO_Geometry in Oracle 10gR2
    Spatial Sorting of Data via Morton Key
    Swapping Ordinates in an SDO_GEOMETRY object
    New To_3D Function
    Extend (Reduce/Contract/Skrink) Function for Oracle
    Loading and Processing GPX 1.1 files using Oracle XMLDB
    Loading Spatial Data from an external CSV file in Oracle
    Calling the Oracle Spatial shapefile loader from within the Oracle database itself
    Implementing SDO_VertexUpdate/ST_VertexUpdate for Oracle
    Implementing SDO_RemovePoint/ST_RemovePoint for Oracle
    Implementing SDO_AddPoint/ST_AddPoint for Oracle
    ESRI ArcSDE Exverted and Inverted Polygons and Oracle Spatial
    Funky Fix Ordinates By Formula
    Implementing a SetPoint/ST_SetPoint function in Oracle
    Implementing an ST_SnapToGrid (PostGIS) function for Oracle Spatial
    Generating random point data
    Implementing an Affine/ST_Affine function for Oracle Spatial
    Implementing a Scale/ST_Scale function for Oracle Spatial
    Implementing a Parallel/ST_Parallel function for linestring data for Oracle Spatial
    Implementing a Rotate/ST_Rotate function for Oracle Spatial
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    Implementing a Translate/ST_Translate/Move function for Oracle Spatial
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    How to extract elements from the result of an sdo_intersection of two polygons.
    How to restart a database after failed parameter change
    Fixing failed spatial indexes after import using data pump
    generate_series: an Oracle implementation in light of SQL Design Patterns
    Multi-Centroid Shootout
    Oracle Spatial Centroid Shootout
    On the use of ROLLUP in Oracle SELECT statements
    Surrounding Parcels
    Spatial Pipelining
    Using Oracle's SDO_NN Operator - Some examples
    Converting distances and units of measure in Oracle Locator
    Split Sdo_Geometry Linestring at a known point
    Forcing an Sdo_Geometry object to contain only points, lines or areas
    Unpacking USER_SDO_GEOM_METADATA's DIMINFO structure using SQL
    Generating multi-points from single point records in Oracle Spatial
    Object Tables of Sdo_Geometry
    Oracle Locator vs Oracle Spatial: A Reflection on Oracle Licensing of the SDO_GEOM Package
    FAST REFRESHing of Oracle Materialized Views containing Sdo_Geometry columns
    Australian MGA/AMG Zone Calculation from geographic (longitude/latitude) data
    Loading Shapefiles (SHP) into Oracle Spatial
    Oracle Spatial Mapping and Map Rendering Performance Tips
    The significance of sdo_lb/sdo_ub in USER_SDO_GEOM_METDATA: Do I need it?
    Oracle Spatial Forum - Melbourne April 2007
    Layer_GTypes for spatial indexes
    Oracle's SQL/MM Compliant Types
    Tips and Tricks



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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.

Playing around with Centroids by using different seed values

Monday February 29 2016 at 13:14

Keywordsrandom x seed generation centroid

Demonstration of different X seed positions for the Centroid_A function.

The CENTROID package that I make available for free exposes a function for generating centroids of polygon (or area) objects.

Here is the function:

  1.   /* ----------------------------------------------------------------------------------------
  2.   * @function   : centroid_a
  3.   * @precis     : Generates centroid for a polygon.
  4.   * @version    : 1.3
  5.   * @description: The standard mdsys.sdo_geom.sdO_centroid function does not guarantee
  6.   *               that the centroid it generates falls inside the polygon.
  7.   *               This function ensures that the centroid of any arbitrary polygon falls within the polygon.
  8.   * @param      : p_geometry     : MDSYS.SDO_GEOMETRY : The geometry object.
  9.   * @param      : P_Method       : pls_integer
  10.   *                              : 0 = Use average of all Area's vertices for starting X centroid calculation
  11.   *                                1 = Use centre X of MBR
  12.   *                                2 = User supplied starting seed X
  13.   *                                3 = Use Standard Oracle centroid function
  14.   *                                4 = Use Oracle implementation of PointOnSurface
  15.   * @param      : p_seed_x       : Number : Starting X ordinate for which a Y that is inside the polygon is returned.
  16.   * @param      : P_Dec_Places   : pls_integer : Ordinate rounding precision for X, Y ordinates.
  17.   * @param      : P_Tolerance    : number      : Tolerance for Oracle functions.
  18.   * @param      : p_loops        : pls_integer : Number of attempts to find centroid based on small changes to seed
  19.   * @return     : centroid       : MDSYS.SDO_GEOMETRY : The centroid.
  20.   * @requires   : GetVector()
  21.   * @history    : Simon Greener - Jul 2008 - Original coding of centroid_a as internal function
  22.   * @history    : Simon Greener - Jan 2012 - Exposed internal function. Added p_seed_x support.
  23.   * @copyright  : Free for public use
  24.   **/
  25.   FUNCTION Centroid_A(P_Geometry   IN Mdsys.Sdo_Geometry,
  26.                       P_Method     IN Pls_Integer DEFAULT 1,
  27.                       P_Seed_X     IN NUMBER      DEFAULT NULL,
  28.                       P_Dec_Places IN Pls_Integer DEFAULT 3,
  29.                       P_Tolerance  IN Pls_Integer DEFAULT 0.05,
  30.                       p_loops      IN pls_integer DEFAULT 10)

If you call the function with its defaults, the p_method parameter will be 1. For this value, the code determines the X ordinate extent of the polygon’s MBR, and selects the middle value as a starting point. If the centroid can be determined with this value, the function returns that value. If it cannot it will randomly generate a new X ordinate value between the minimum and maximum value. It will do this for as many times as it needs to up to the p_loop parameter value.

If this is not acceptable, you can generate your own starting X value. The following SQL shows how to do this for two polygons.

  3.          SDO_GEOMETRY(2003,2154,SDO_POINT_TYPE(302941.0,6669203.45,NULL),SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(297360.0,6667914.0, 297660.0,6667653.0, 298609.0,6666944.0, 299789.0,6664881.0, 300680.0,6664235.0, 301667.0,6664862.0, 303232.0,6664738.0, 304687.0,6663414.0, 304945.0,6663116.0, 305198.0,6662814.0, 306251.0,6661156.0, 307301.0,6657791.0, 308037.0,6656883.0, 308202.0,6657247.0, 308522.0,6661532.0, 307817.0,6662929.0, 305833.0,6664168.0, 305510.0,6664375.0, 303260.0,6665837.0, 302505.0,6665938.0, 302397.0,6666285.0, 302495.0,6667977.0, 301563.0,6668110.0, 301929.0,6668266.0, 303324.0,6667787.0, 303670.0,6668397.0, 303702.0,6669597.0, 303379.0,6670300.0, 302298.0,6670765.0, 301143.0,6671816.0, 300762.0,6671916.0, 299584.0,6671989.0, 297610.0,6671815.0, 298172.0,6670055.0, 297408.0,6668688.0, 297360.0,6667914.0))
  4.            AS POLYGON
  7.          SDO_GEOMETRY(2003,2154,SDO_POINT_TYPE(360179.0,6575409.45,NULL),SDO_ELEM_INFO_ARRAY(1,1003,1),SDO_ORDINATE_ARRAY(359878.0,6574428.0, 360194.0,6574227.0, 361803.0,6573283.0, 363464.0,6571791.0, 363700.0,6571492.0, 364187.0,6570906.0, 366530.0,6569742.0, 367624.0,6569426.0, 369521.0,6569568.0, 369878.0,6569424.0, 371622.0,6571410.0, 370159.0,6571358.0, 369671.0,6572729.0, 369472.0,6573056.0, 368841.0,6574386.0, 368122.0,6574650.0, 367017.0,6574363.0, 365341.0,6575902.0, 365027.0,6576142.0, 363611.0,6576780.0, 360865.0,6576508.0, 360487.0,6576519.0, 359009.0,6576823.0, 357554.0,6577889.0, 359387.0,6578390.0, 359775.0,6579403.0, 356629.0,6579554.0, 355793.0,6578505.0, 354495.0,6577699.0, 354353.0,6577326.0, 353535.0,6577430.0, 352627.0,6578530.0, 352221.0,6580046.0, 352254.0,6580505.0, 352397.0,6580138.0, 352782.0,6579453.0, 353155.0,6579362.0, 353703.0,6580730.0, 354082.0,6580648.0, 354163.0,6579933.0, 354515.0,6579796.0, 355125.0,6580194.0, 354737.0,6581702.0, 353718.0,6582869.0, 352553.0,6583035.0, 351635.0,6582314.0, 350259.0,6581598.0, 348736.0,6581698.0, 348873.0,6580572.0, 349939.0,6578955.0, 350054.0,6578581.0, 350563.0,6577117.0, 352612.0,6576013.0, 355156.0,6576764.0, 355539.0,6576787.0, 359878.0,6574428.0))
  8.            AS polygon      
  9.     FROM dual
  10. )
  11. -- select poly_id,a.polygon,CENTROID.CENTROID_A(a.POLYGON,0,null,2,2,2) as cPoly from poly a;
  12. , X_EXTENT AS (
  14.          D.ROW_ID,
  15.          MINX + ((MAXX-MINX)/50)*ROW_ID AS INC,
  16.          C.POLYGON,
  17.          sdo_geometry(2002,c.polygon.sdo_srid,NULL,sdo_elem_info_array(1,2,1),sdo_ordinate_array(minx,miny,maxx,miny)) AS mbr_baseline
  18.     FROM (SELECT b.POLY_ID,
  19.                  SDO_GEOM.SDO_MIN_MBR_ORDINATE(MBR,1) AS MINX,
  20.                  SDO_GEOM.SDO_MIN_MBR_ORDINATE(MBR,2) AS MINY,
  21.                  SDO_GEOM.SDO_MIN_MBR_ORDINATE(MBR,3) AS MAXX,
  22.                  b.polygon
  23.             FROM (SELECT P.POLY_ID, p.polygon, SDO_GEOM.SDO_MBR(P.POLYGON) AS MBR
  24.                     FROM POLY P
  25.                  ) B
  26.           ) c,
  27.           (SELECT level AS row_id FROM dual CONNECT BY level < 50) d
  28. )
  29. SELECT a.POLY_ID, a.row_id, CENTROID.CENTROID_A(a.POLYGON,2,a.INC,2,2,2), mbr_baseline
  30.   FROM X_EXTENT a
  31.   ORDER BY a.poly_id, a.row_id;

The different centroid values are displayed in the following two images. The actual centroid created by the CENTROID_A function with the default p_method value is shown in red.

I hope this is of help to someone out there.

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