SDO_GEOM.SDO_CONVEXHULL

Format

SDO_GEOM.SDO_CONVEXHULL(     
  geom1  IN SDO_GEOMETRY,      
  dim1   IN SDO_DIM_ARRAY      
) RETURN SDO_GEOMETRY;

or

SDO_GEOM.SDO_CONVEXHULL(     
  geom1  IN SDO_GEOMETRY,      
  tol    IN NUMBER       
) RETURN SDO_GEOMETRY;

Description

Returns a polygon-type object that represents the convex hull of a geometry object.

Parameters

geom1: Geometry object.
dim1: Dimensional information array corresponding to geom1, usually selected from one of the xxx_SDO_GEOM_METADATA views (described in Geometry Metadata Views).
tol: Tolerance value (see Tolerance).

Usage Notes

The convex hull is a simple convex polygon that completely encloses the geometry object. Spatial uses as few straight-line sides as possible to create the smallest polygon that completely encloses the specified object. A convex hull is a convenient way to get an approximation of a complex geometry object.

If the geometry (geom1) contains any arc elements, the function calculates the minimum bounding rectangle (MBR) for each arc element and uses these MBRs in calculating the convex hull of the geometry. If the geometry object (geom1) is a circle, the function returns a square that minimally encloses the circle.

The function returns a null value if geom1 is of point type, has fewer than three points or vertices, or consists of multiple points all in a straight line.

With geodetic data, this function is supported by approximations, as explained in Functions Supported by Approximations with Geodetic Data.

Examples

The following example returns a geometry object that is the convex hull of cola_c. (The example uses the definitions and data from Simple Example: Inserting_ Indexing_ and Querying Spatial Data. This specific example, however, does not produce useful output—the returned polygon has the same vertices as the input polygon—because the input polygon is already a simple convex polygon.)

-- Return the convex hull of a polygon.
SELECT c.name, SDO_GEOM.SDO_CONVEXHULL(c.shape, m.diminfo) 
  FROM cola_markets c, user_sdo_geom_metadata m 
  WHERE m.table_name = 'COLA_MARKETS' AND m.column_name = 'SHAPE' 
  AND c.name = 'cola_c';

NAME                                                                            
--------------------------------                                                
SDO_GEOM.SDO_CONVEXHULL(C.SHAPE,M.DIMINFO)(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, 
--------------------------------------------------------------------------------
cola_c                                                                          
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 1), SDO_ORDINATE_ARR
AY(6, 3, 6, 5, 4, 5, 3, 3, 6, 3))