Howto verify SPATIAL functions/operators results with Geodetic Data
Last updated on FEBRUARY 13, 2018
Applies to:Oracle Spatial and Graph - Version 126.96.36.199 to 188.8.131.52 [Release 9.2 to 11.2]
Information in this document applies to any platform.
The Goal of this document is to show a way to verify SPATIAL functions/operators results, with Geodetic Data, by visualization.
Before we start, here are some common explanations.
SPATIAL functions/operators results and its visualization with Geodetic Data
Effective with Oracle9i, Spatial provides a rational and complete treatment of geodetic coordinates. Before Oracle9i, Spatial computations were based solely on flat (Cartesian) Map 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 the Earth in the specified geodetic coordinate system and return correct, accurate results.
As long as it's “Non-Geodetic Data” we speak about, we can simply visualize the Geometries with Mapviewer.
But sometimes we run into the situation, where somebody has doubts on the reliability of the SPATIAL functions/operators like for example SDO_RELATE.
And when it's geodetic data that needs to be processed, it's not an easy task to verify the function's/operator’s results as Mapviewer does not take any attention geodetic reference(SRID).
Before we start to describe the verification process, here we provide the simplified definition
of the term "Great Circle" which is used further on in the solutions description.
On the idealized surface of the Earth, the shortest distance between two points lies along a “great circle”.
So the “great circle” is the "earth related" equivalent of a straight line in flat(Cartesian) Map.
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