[postgis-devel] Oracle SDO_GEOMETRY vs PostGIS WKT

[Jorge Arévalo]

On Wed, Aug 25, 2010 at 3:30 PM, Nicklas Avén
<nicklas.aven at jordogskog.no> wrote:
> 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?
>

Absolutely clear. Many thanks for the great explanation. Now, I
understand that Oracle uses a "topological storage model", different
to its another model (with SDO_GEOMETRY, for example). Anyway, maybe
the fact Oracle has a topological storage model different to the other
one, is not related with the apparent complication (at least for me)
of the SDO_GEOMETRY format. Or maybe it's not really complicated, or
maybe only Oracle knows the reason...

The fact it's I find working with the "standard" oracle spatial
objects (like SDO_GEOMETRY) more difficult than working with PostGIS
and WKT Raster. Coming from a beginner in both extensions.


> 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.
>
Yep, understood. Thanks again.


> 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?
>
Yes, you're right. Today, I've learnt a new thing :-)

> 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?
>
Ctrl+D

Jorge

> /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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