[postgis-devel] Oracle SDO_GEOMETRY vs PostGIS WKT

[Martin Davis]

No, the Oracle geometry model is not topological.  It is based on 
exactly the same approach as PostGIS, ESRI and Microsoft use for their 
geometry implementations.  Vertices and edges are not shared, they are 
duplicated whereever they occur.

Oracle does have a topological storage model as others have pointed out, 
but this historically was released after SDO_GEOMETRY and I think has 
only minor connections with it.

I think the reason why Oracle's Geometry model appears complicated are:

- it is quite general (e.g supporting arbitrary curvilinear segments)

- for whatever reason they chose to expose the underlying implementation 
structure (both in terms of API and in documentation).  PostGIS and 
other systems don't expose this model directly to the user.  If you saw 
the underlying PostGIS model you'd probably think it was even MORE 
complicated!

M

Nicklas Avén wrote:
> Hallo
>
>   
>> Yep, like other companies developing propietary software. The point is
>> I don't understand why using a mix of numbers and arrays whose
>> elements index tables to simply represent a polygon. Saving storage
>> space? I don't know. The PostGIS way, closer to OGC standard, is much
>> easier, IMHO.
>>
>>     
>
> I don't know what this Oracle representation looks like but from above it sounds like it might be about some topological model. 
> In PostGIS representation I guess it is difficult to describe two neighbor polygons without repeating the shared vertexes for both polygons?
>
> /Nicklas
>
>
>
>   
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022