6.10 Notes and Restrictions with Coordinate Systems Support

The following notes and restrictions apply to coordinate systems support in the current release of Oracle Spatial.

If you have geodetic data, see Geodetic Coordinate Support for additional considerations, guidelines, and restrictions.

• Different Coordinate Systems for Geometries with Operators and Functions
  
• 3D LRS Functions Not Supported with Geodetic Data
  
• Functions Supported by Approximations with Geodetic Data
  
• Unknown CRS and NaC Coordinate Reference Systems
  

6.10.1 Different Coordinate Systems for Geometries with Operators and Functions

For spatial operators (described in Spatial Operators ) that take two geometries as input parameters, if the geometries are based on different coordinate systems, the query window (the second geometry) is transformed to the coordinate system of the first geometry before the operation is performed. This transformation is a temporary internal operation performed by Spatial; it does not affect any stored query-window geometry.

For SDO_GEOM package geometry functions (described in SDO_GEOM Package (Geometry)) that take two geometries as input parameters, both geometries must be based on the same coordinate system.

6.10.2 3D LRS Functions Not Supported with Geodetic Data

In the current release, the 3D formats of LRS functions (explained in 3D Formats of LRS Functions) are not supported with geodetic data.

6.10.3 Functions Supported by Approximations with Geodetic Data

In the current release, the following functions are supported by approximations with geodetic data:

• SDO_GEOM.SDO_BUFFER

• SDO_GEOM.SDO_CENTROID

• SDO_GEOM.SDO_CONVEXHULL

When these functions are used on data with geodetic coordinates, they internally perform the operations in an implicitly generated local-tangent-plane Cartesian coordinate system and then transform the results to the geodetic coordinate system. For SDO_GEOM.SDO_BUFFER, generated arcs are approximated by line segments before the back-transform.

6.10.4 Unknown CRS and NaC Coordinate Reference Systems

The following coordinate reference systems are provided for Oracle internal use and for other possible special uses:

• unknown CRS (SRID 999999) means that the coordinate system is unknown, and its space could be geodetic or Cartesian. Contrast this with specifying a null coordinate reference system, which indicates an unknown coordinate system with a Cartesian space.

• NaC (SRID 999998) means Not-a-CRS. Its name is patterned after the NaN (Not-a-Number) value in Java. It is intended for potential use with nonspatial geometries.

The following restrictions apply to geometries based on the unknown CRS and NaC coordinate reference systems:

• You cannot perform coordinate system transformations on these geometries.

• Operations that require a coordinate system will return a null value when performed on these geometries. These operations include finding the area or perimeter of a geometry, creating a buffer, densifying an arc, and computing the aggregate centroid.