[postgis-devel] Oracle SDO_GEOMETRY vs PostGIS WKT

[Andrea Peri]

>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
http://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,

-- 
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Andrea Peri
. . . . . . . . .
qwerty àèìòù
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