[Java-collab] Introduction

[Markus Schneider]

Jody,

AFAIK, PostGIS cannot evaluate spatial predicates on curves yet!? I know, it supports circle segments, but the operators
were not implemented last time I checked. Also, there's more to GML curves then circle segments (e.g. splines,
clothoids, ...).

As I see it, a major challenge is finding a feasible interpolation criterion, i.e. how to determine out the number of
required points in the line string representation.

Best regards,
Markus

Jody Garnett wrote:
> Very Fun Markus:
> 
> The approach to curves matches what I had in mind; I was going to do it
> as an extension to JTS Geometry but that is more of interest if we
> wanted to keep working with JTS Geometry API.
> 
> In anycase this sounds like a great area for collaboration; the iso19107
> geometry api is not intergrated into geotools at the moment so both ways
> forward represent similar amounts of work. We actually have a team
> looking at doing this work over the next two years (so it would be good
> to sort out a way forward).
> 
> As for PostGIS; if you can store your origional curve in the new
> extensions to WKB can you just drop your linearized representation (ie
> there is no point in storing it...).
> 
> Jody
> 
> On 30/06/2009, at 1:02 AM, Markus Schneider wrote:
> 
>> As Andrea already knows, we're trying to keep the implementation
>> effort as low as possible. Therefore, our approach is
>> not extending JTS, but using wrappers around JTS geometries, that can
>> cope with simple and complex geometries:
>>
>> - In case of a simple geometry (Point, LineString, Polygon), the
>> wrapper is totally straightforward, e.g. calls to
>> #intersects() are just passed to JTS.
>> - For complex ones (e.g. curves with non-linear segments), the curve
>> parameters are stored in the wrapper and
>> additionally, a linearized version is generated (represented using
>> JTS) that is used to evaluate spatial predicates.
>>
>> A major benefit of this approach is that it is also applicable to
>> backends (e.g. PostGIS). We would store a linearized
>> version as a native PostGIS geometry (used for the topological
>> predicates), and store a BLOB beside it that stores the
>> original curve segments and their parameters (only necessary when
>> curve is not a linestring).
>>
>> Obviously, this approach is restriced to operations on the footprint
>> when dealing with 3D-geometries. But this is still
>> better than nothing :-) Getting a 3D-BBox-operator working should be
>> manageble, though.
>>
>> Best regards,
>> Markus
>>
>> Andrea Aime wrote:
>>> Jody Garnett ha scritto:
>>>> Note I am serious about the Curve thing...
>>>> - It is strategic work - supporting the WKB format
>>>> - PostGIS / GEOS is starting moving on it
>>>> - JTS won't touch it so it is up to us :-D
>>>>
>>>> Mark Leslie and myself had some blog posts on it a couple months back;
>>>> another idea in search of time/funds/hapless volunteer :-D
>>>>
>>>> It also makes sense to walk before we can run; Curve is a smaller
>>>> problem then Geometry and is not one currently addressed?
>>>
>>> Jody, DeeGree has this nice geometry library and they are interested
>>> is sharing the load on it as a whole. I believe it's well worth looking
>>> into.
>>>
>>> Cheers
>>> Andrea
>>>
>>
>>
>> -- 
>> 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
>>
>> _______________________________________________
>> Java-collab mailing list
>> Java-collab at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/java-collab
> 


-- 
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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