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

Understanding linear referencing and measures


All geographic representations stored in the SDO_GEOMETRY object are just that: representations. The linestring describing a pipe is not the pipe; the linestring describing a road in a GPS in-car navigation unit is not the road: they are scale-dependent representations of the middle of the pipe (an imaginary line drawn down the center of the pipe) or the middle of a marked lane for traffic on a road.

By scale-dependent is meant that the position of each vertex in the linestring has a locational "vagueness". The amount of location vagueness depends on the source of its measurement. A position measured by a surveyor using a modern electronic theodolite may be accurate to +/- 5mm; a GPS observation +/- 10cm; an old 1:1000 map from a roads department, +/- 2m.

Regardless as to capture method, each linestring's representation has an implicit length (measured by SDO_GEOM.Sdo_Length or the T_GEOMETRY.ST_Length method) property, but this length is also...