Oracle Spatial User's Guide and Reference - InfoLab

6.1.8 Transformation
Geodetic Coordinate Support
Transformation is the conversion of coordinates from one coordinate system to
another coordinate system.
If the coordinate system is georeferenced, transformation can involve datum
transformation: the conversion of geodetic coordinates from one geodetic datum to
another geodetic datum, usually involving changes in the shape, orientation, and
center position of the reference ellipsoid.
6.2 Geodetic Coordinate Support
Effective with Oracle9i, Spatial provides a rational and complete treatment of
geodetic coordinates. Before Oracle9i, Spatial computations were based solely on
flat (Cartesian) coordinates, regardless of the coordinate system specified for the
layer of geometries. Consequently, computations for data in geodetic coordinate
systems were inaccurate, because they always treated the coordinates as if they
were on a flat surface, and they did not consider the curvature of the surface.
Effective with release 9.2, ellipsoidal surface computations consider the curvatures
of arcs in the specified geodetic coordinate system and return correct, accurate
results. In other words, Spatial queries return the right answers all the time.
6.2.1 Geodesy and Two-Dimensional Geometry
A two-dimensional geometry is a surface geometry, but the important question is:
What is the surface? A flat surface (plane) is accurately represented by Cartesian
coordinates. However, Cartesian coordinates are not adequate for representing the
surface of a solid. A commonly used surface for spatial geometry is the surface of
the Earth, and the laws of geometry there are different than they are in a plane. For
example, on the Earth’s surface there are no parallel lines: lines are geodesics, and
all geodesics intersect. Thus, closed curved surface problems cannot be done
accurately with Cartesian geometry.
Spatial provides accurate results regardless of the coordinate system or the size of
the area involved, without requiring that the data be projected to a flat surface. The
results are accurate regardless of where on the Earth’s surface the query is focused,
even in "special" areas such as the poles. Thus, you can store coordinates in any
datum and projections that you choose, and you can perform accurate queries
regardless of the coordinate system.
Coordinate Systems (Spatial Reference Systems) 6-3