Book Image

Applying and Extending Oracle Spatial

Book Image

Applying and Extending Oracle Spatial

Overview of this book

Spatial applications should be developed in the same way that users develop other database applications: by starting with an integrated data model in which the SDO_GEOMETRY objects are just another attribute describing entities and by using as many of the database features as possible for managing the data. If a task can be done using a database feature like replication, then it should be done using the standard replication technology instead of inventing a new procedure for replicating spatial data. Sometimes solving a business problem using a PL/SQL function can be more powerful, accessible, and easier to use than trying to use external software. Because Oracle Spatial's offerings are standards compliant, this book shows you how Oracle Spatial technology can be used to build cross-vendor database solutions. Applying and Extending Oracle Spatial shows you the clever things that can be done not just with Oracle Spatial on its own, but in combination with other database technologies. This is a great resource book that will convince you to purchase other Oracle technology books on non-spatial specialist technologies because you will finally see that "spatial is not special: it is a small, fun, and clever part of a much larger whole".
Table of Contents (20 chapters)
Applying and Extending Oracle Spatial
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Preface
Table Comparing Simple Feature Access/SQL and SQL/MM–Spatial
Index

Extracting and filtering SDO_GEOMETRY elements


As we have seen, often the processing of an object cannot occur unless its SDO_ELEM_INFO attribute informs an algorithm's decision making. This section will explore the extraction of various elements and subelements from different geometry objects by processing the SDO_ELEM_INFO array.

Introducing the Oracle SDO_UTIL.Extract function

The Oracle API from 10gR1 onwards provides the SDO_UTIL.Extract element extraction function. The function is as follows:

 SDO_UTIL.Extract(
     geometry In SDO_GEOMETRY,
     element  In NUMBER,
     ring     In NUMBER DEFAULT 0
) Return SDO_GEOMETRY;
  • Geometry: [Two dimensional] geometry from which to extract the [Return] geometry.

  • Element: Number of the element in the geometry: 1 for the first [...], 2 for the second [...], and so on. Geometries with SDO_GTYPE values [...] ending in 1, 2, or 3 have one element; [...] ending in 4, 5, 6, or 7 can have more than one element. For example, a [2007] multipolygon […] might...