[Java-collab] Re: Collab on Geometry

[Markus Schneider]

Hello again,

just wanted to point you to our wiki page on the geometry model design (which currently does not include any more
information than provided in the last mail): https://wiki.deegree.org/deegreeWiki/deegree3/Geometry

Any edits are welcome.

Best regards,
Markus

Markus Schneider wrote:
> Hello Jody and others,
> 
> sorry for the delay. I am all ears now.
> 
> I guess we could start with a breakout IRC session -- preferrably at the beginning of next week, when Rutger Bezema from
> deegree is available again.
> 
> It may however be worthwhile to present our ideas of the target requirements on the mailing list first. Here's our side
> of the story (for now):
> 
> - Support every (vector?!) geometry-construct from GML 3.1.1 (and GML 3.2.1), so it's for example possible to read in
> arbitrary GML (geometry) documents and have a faithful in-memory representation.
> 
> - Support 2D and 3D space. Andrea said he is keen of having support for measures as well. Would 4D be enough? Or should
> we just keep this unconstrained?
> 
> - Keep the overhead (compared to using JTS directly) as low as possible: for simple geometries the geometry model would
> probably just act as a thin wrapper around JTS.
> 
> - Support topological predicates using JTS. For not-natively supported geometries, a linearized version (curves) would
> be used for the predicate evaluation. For 3D geometries, this has it limitations, but it should be possible to support
> tests on the footprint and provide a full-3D bbox operator.
> 
> - Represent referenced geometries (xlink) as in the following example ). Note the pointProperty elements in the
> LineString element:
> 
> <MultiGeometry srsName="EPSG:4326" xmlns="http://www.opengis.net/gml"
>   xmlns:gml="http://www.opengis.net/gml" xmlns:xlink="http://www.w3.org/1999/xlink"
>   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>   xsi:schemaLocation="http://www.opengis.net/gml http://schemas.opengis.net/gml/3.1.1/base/gml.xsd">
>   <geometryMembers>
>     <Point gml:id="P1">
>       <coord>
>         <X>0.0</X>
>         <Y>0.0</Y>
>       </coord>
>     </Point>
>     <Point gml:id="P2">
>       <coord>
>         <X>1.0</X>
>         <Y>1.0</Y>
>       </coord>
>     </Point>
>     <LineString gml:id="L1">
>       <pointProperty xlink:href="#P1" />
>       <pointProperty>
>         <Point>
>           <pos>1.0 0.0</pos>
>         </Point>
>       </pointProperty>
>       <pointProperty xlink:href="#P2" />
>       <pointProperty>
>         <Point>
>           <pos>0.0 1.0</pos>
>         </Point>
>       </pointProperty>
>     </LineString>
>   </geometryMembers>
> </MultiGeometry>
> 
> Note that the xlinks could also be pointing to external resources.
> 
> - Design an efficient binary format so the complex geometries can be stored in today's spatial backends (e.g. PostGIS).
> As already mentioned, the trick would be to delegate predicates to the (linearized) native geometry column and use the
> BLOB for reconstructing the original one.
> 
> The existing codebase already implements some of the mentioned requirements (except predicates and backend format).
> There's also a quite comprehensive test suite for all kinds of GML geometry constructs.
> 
> Ready for your comments / additions.
> 
> Best regards,
> Markus
> 
> Jody Garnett wrote:
>> Hi Markus:
>>
>> I got a bit distracted by the fun technical details and missed the
>> important part.
>>
>> First of all thanks you to both Andrea and yourself for sitting down
>> and talking about collaboration. Sounds like it was an excellent
>> sprint.
>>
>> Secondly - I am very keen to collaborate on the 3D Geometry front; and
>> belive that others in the GeoTools community will be interested as
>> well. What is a sensible next step? We traditionally make use of
>> "breakout IRC" sessions; or should I hunt down interested parties and
>> ask them to join this email list?
>>
>> Jody
> 
> 
> 
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-- 
Markus Schneider

l a t / l o n  GmbH
Aennchenstrasse 19           53177 Bonn, Germany
phone ++49 +228 184960       fax ++49 +228 1849629
http://www.lat-lon.de        http://www.deegree.org

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