[postgis-devel] Oracle SDO_GEOMETRY vs PostGIS WKT

Jorge Arévalo jorge.arevalo at deimos-space.com
Thu Aug 26 03:35:42 PDT 2010


On Wed, Aug 25, 2010 at 5:41 PM, Martin Davis <mbdavis at refractions.net> wrote:
> 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

So, with PostGIS you can simply work with WKT format, and avoid the
internals. Oracle does support WKT/WKB format for creating [1] and
exporting [2], but they expose the internals, and force the user to
work with them. Ok. Many thanks!

Jorge

[1] http://download.oracle.com/docs/cd/B28359_01/appdev.111/b28400/sdo_objrelschema.htm#CBBFGHAE
[2] http://download.oracle.com/docs/cd/B28359_01/appdev.111/b28400/sdo_util.htm#BJEBJEGJ

>
> 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
>
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>



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Jorge Arévalo
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