[postgis-devel] Oracle SDO_GEOMETRY vs PostGIS WKT

[Nicklas Avén]

Andrea

Do you have any answer to Jorges initial question why the Oracle geometry representation (sdo_geometry) seems so complicated if it is not about topology? 

Jorge

As Paul said the storage is something else, but it can not be a topological model in the background that "user" never sees. The "user" in this case is any client software and the client software is to do editing in one polygon it has to be aware of how that effects the neighbor. If the storage is in  a topological storage model moving one vertex will need a decision how to handle the polygon on the other side of the edge. If it is stored in PostGIS you can do whatever you want with one polygon and the neighbor will not be affected.

One reason for a topological storage model is maybe speed for analysis and processing, but isn't a main reason also a way of keeping the topology without a lot of functions searching for holes and so on?

Is the PostGIS project:
http://trac.osgeo.org/postgis/wiki/UsersWikiPostgisTopology
alive in some way. I see Sandro checked in the readme, is he the author of the project?

/Nicklas


2010-08-25 Andrea Peri  wrote:

>Sorry if the question sounds "silly", but as I understand it, both
>>extensions (PostGIS and Oracle Spatial) provide topological
>>operations, so, they both have topological models to define
>>relationships between objects. My point is I think Oracle uses a more
>>complicated way to define these objects (for example, a polygon).
>>
>>I don't really think the reason is the Oracle's way is better for 
>>kind of operations (calculate intersections, or whatever), because I'm
>>talking about the way of representing data for the user, not the way
>>the data are stored.
>They are two question quite difference.
>
>A question is to be capable of topological operation. This is possible with oracle and with postgis.
>
>Another question is use a "topological store model". This is possible for oracle but not for postgis. There is a topology package for postgis but it seem to be too early.
>
>A "topological store model" is a technic to store the data using three tables:
>
>a table for faces, a table for edges and a table for nodes.
>
>like oracle 
>download.oracle.com/docs/cd/B19306_01/appdev.102/b14256/sdo_topo_concepts.htm#BABBBDBJ
>
>But to have this you must don't use the SDO_GFeometry but instead the SDO_Topo_Geometry.
>
>With a sdo_topo_geometry when you put a polygon, it is split in 1 face, some edge and some node.
>The most know properties of a topological model od storing data is that one edge can be owned from one or two faces.
>
>So is usually say that a topological model is more efficient because use one only lines instead of two lines overlapped (one for each of the two touching polygons), and when the user change an edge (a line)
>the change is inherited even from the boundary of the two faces (two polygon).
>
>This is even for nodes over the edges and so on...
>
>But...
>is no easy work with the Oracle Topological model ....
>
>And I don't know NO ONE tool gis to support the Oracle Topological.
>
>Every tools, (esri, intergraph, qgis, and so on)
>support only the geometry Model (sdo_geometry) 
>absolutely do not support the oracle topological model (sdo_topo_geometry)
>
>So use the oracle topology , mean work using many query sql.
>
>Regards, 
>
>-- 
>-----------------
>Andrea Peri
>. . . . . . . . . 
>qwerty àèìòù
>-----------------
>
>
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