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SDO_GEOM.SDO_BUFFER
Usage Notes
Examples
■ arc_tolerance and an arc tolerance value. See the Usage Notes for the SDO_
GEOM.SDO_ARC_DENSIFY function in this chapter for more information about
the arc_tolerance keyword.
For example: 'unit=km arc_tolerance=0.05'
If the input geometry is geodetic data and if arc_tolerance is not specified, the
default value is the tolerance value multiplied by 20. Spatial uses the arc_tolerance
value to perform arc densification in computing the result. If the input geometry is
Cartesian or projected data, arc_tolerance has no effect and should not be
specified.
If this parameter is not specified for a Cartesian or projected geometry, or if the arc_
tolerance keyword is specified for a geodetic geometry but the unit keyword is not
specified, the unit of measurement associated with the data is assumed.
This function returns a geometry object representing the buffer polygon.
This function creates a rounded buffer around a point, line, or polygon, or inside a
polygon. The buffer within a void is also rounded, and is the same distance from the
inner boundary as the outer buffer is from the outer boundary. See Figure 1–7 for an
illustration.
If the buffer polygon geometry is in a projected coordinate system, it will contain arcs;
and if you want to transform that geometry to a geodetic coordinate system, you must
first densify it using the SDO_GEOM.SDO_ARC_DENSIFY function, and then
transform the densified geometry.
With geodetic data, this function is supported by approximations, as explained in
Section 6.10.3.
With geodetic data, this function should be used only for relatively small geometries:
geometries for which the local tangent plane projection that is used for internal
computations does not introduce significant distortions or errors. This limits the
applicable domain of source geometries, whether line strings or polygons, to
approximately the area of Texas (United States), France, or Manchuria province
(China).
The following example returns a polygon representing a buffer of 1 around cola_a.
Note the rounded corners (for example, at .292893219,.292893219) in the returned
polygon. (The example uses the non-geodetic definitions and data from Section 2.1.)
-- Generate a buffer of 1 unit around a geometry.
SELECT c.name, SDO_GEOM.SDO_BUFFER(c.shape, m.diminfo, 1)
FROM cola_markets c, user_sdo_geom_metadata m
WHERE m.table_name = 'COLA_MARKETS' AND m.column_name = 'SHAPE'
AND c.name = 'cola_a';
NAME
--------------------------------
SDO_GEOM.SDO_BUFFER(C.SHAPE,M.DIMINFO,1)(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, Z)
-------------------------------------------------------------------------------cola_a
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1005, 8, 1, 2, 2, 5, 2, 1,
7, 2, 2, 11, 2, 1, 13, 2, 2, 17, 2, 1, 19, 2, 2, 23, 2, 1), SDO_ORDINATE_ARRAY(
0, 1, .292893219, .292893219, 1, 0, 5, 0, 5.70710678, .292893219, 6, 1, 6, 7, 5.
70710678, 7.70710678, 5, 8, 1, 8, .292893219, 7.70710678, 0, 7, 0, 1))
24-12 Oracle Spatial Developer’s Guide