SDO_GEOM.SDO_ARC

Format

SDO_GEOM.SDO_ARC_DENSIFY(     
  geom    IN SDO_GEOMETRY,      
  dim     IN SDO_DIM_ARRAY       
  params  IN VARCHAR2      
) RETURN SDO_GEOMETRY;

or

SDO_GEOM.SDO_ARC_DENSIFY(
  geom    IN SDO_GEOMETRY,      
  tol     IN NUMBER       
  params  IN VARCHAR2      
) RETURN SDO_GEOMETRY;

Description

Returns a geometry in which each circular arc in the input geometry is changed into an approximation of the circular arc consisting of straight lines, and each circle is changed into a polygon consisting of a series of straight lines that approximate the circle.

Parameters

geom: Geometry object.
dim: Dimensional information array corresponding to geom, usually selected from one of the xxx_SDO_GEOM_METADATA views (described in Geometry Metadata Views).
tol: Tolerance value (see Tolerance).
params: A quoted string containing an arc tolerance value and optionally a unit value. See the Usage Notes for an explanation of the format and meaning.

Usage Notes

If you have geometries in a projected coordinate system that contain circles or circular arcs, you can use this function to densify them into regular polygons. You can then use the resulting straight-line polygon geometries for any spatial operations, or you can transform them to any projected or geodetic coordinate system.

The params parameter is a quoted string that can contain the arc_tolerance keyword, as well as the unit keyword to identify the unit of measurement associated with the arc_tolerance value. For example:

'arc_tolerance=0.05 unit=km'

The arc_tolerance keyword specifies, for each arc in the geometry, the maximum length of the perpendicular line between the surface of the arc and the straight line between the start and end points of the arc. Figure 25-1 shows a line whose length is the arc_tolerance value for the arc between points A and B.

Figure 25-1 Arc Tolerance

Description of "Figure 25-1 Arc Tolerance"

The arc_tolerance keyword value must be greater than the tolerance value associated with the geometry. (The default value for arc_tolerance is 20 times the tolerance value.) As you increase the arc_tolerance keyword value, the resulting polygon has fewer sides and a smaller area; as you decrease the arc_tolerance keyword value, the resulting polygon has more sides and a larger area (but never larger than the original geometry).

If the unit keyword is specified, the value must be an SDO_UNIT value from the MDSYS.SDO_DIST_UNITS table (for example, 'unit=KM'). If the unit keyword is not specified, the unit of measurement associated with the geometry is used. See Unit of Measurement Support for more information about unit of measurement specification.

Examples

The following example returns the geometry that results from the arc densification of cola_d, which is a circle. (The example uses the definitions and data from Simple Example: Inserting_ Indexing_ and Querying Spatial Data.)

-- Arc densification of the circle cola_d
SELECT c.name, SDO_GEOM.SDO_ARC_DENSIFY(c.shape, m.diminfo, 
                                       'arc_tolerance=0.05') 
  FROM cola_markets c, user_sdo_geom_metadata m 
  WHERE m.table_name = 'COLA_MARKETS' AND m.column_name = 'SHAPE' 
  AND c.name = 'cola_d';

NAME
--------------------------------
SDO_GEOM.SDO_ARC_DENSIFY(C.SHAPE,M.DIMINFO,'ARC_TOLERANCE=0.05')(SDO_GTYPE, SDO_
--------------------------------------------------------------------------------
cola_d
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 1), SDO_ORDINATE_ARR
AY(8, 7, 8.76536686, 7.15224093, 9.41421356, 7.58578644, 9.84775907, 8.23463314,
 10, 9, 9.84775907, 9.76536686, 9.41421356, 10.4142136, 8.76536686, 10.8477591,
8, 11, 7.23463314, 10.8477591, 6.58578644, 10.4142136, 6.15224093, 9.76536686, 6
, 9, 6.15224093, 8.23463314, 6.58578644, 7.58578644, 7.23463314, 7.15224093, 8,
7))