[mapguide-users] OGR / GEOS selection problem
Kenneth, GEOGRAF A/S
ks at geograf.dk
Tue Jun 12 19:11:47 EDT 2007
I've finally built it with GDAL 1.4.1, GEOS 3.0.0rc4, mysql, PostGIS and
SQLite support. No Oracle support though.
It contains Traians latest updates.
http://www.hexad.dk/MapGuide/OGR%20Provider%20Release%20FDO%203.2.2%20-%20Proj%204.5.0%20-%20GDal%201.4.1%20-%20Geos%203.0.0rc4%20-%20No%20OCI%20-%20PostGIS%20-%20MySQL%20-%20SQLite.zip
Regards, Kenneth, GEOGRAF A/S
Traian Stanev skrev:
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> GDAL 1.4.0, GEOS 2.2.3.
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> *From:* mapguide-users-bounces at lists.osgeo.org
> [mailto:mapguide-users-bounces at lists.osgeo.org] *On Behalf Of
> *Kenneth, GEOGRAF A/S
> *Sent:* Tuesday, June 12, 2007 10:55 AM
> *To:* MapGuide Users Mail List
> *Subject:* Re: [mapguide-users] OGR / GEOS selection problem
>
>
>
> What version of the GDal and GEOS did you use?
>
>
> Regards, Kenneth, GEOGRAF A/S
>
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> Traian Stanev skrev:
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> I just tried it on my Australia states data set which has polygons
> with 16000+ vertices. It works fine and it is not slow (less than 1
> second from mouse click to the selected polygon being highlighted in
> the AJAX viewer). May be it is a problem in your configuration. FWIW
> my data came from a SHP file.
>
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> Traian
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> *From:* mapguide-users-bounces at lists.osgeo.org
> <mailto:mapguide-users-bounces at lists.osgeo.org>
> [mailto:mapguide-users-bounces at lists.osgeo.org] *On Behalf Of
> *Kenneth, GEOGRAF A/S
> *Sent:* Tuesday, June 12, 2007 10:36 AM
> *To:* MapGuide Users Mail List
> *Subject:* Re: [mapguide-users] OGR / GEOS selection problem
>
>
>
> Yes, I have tried doing the selection with a triangle, and it also
> works, but there is another bug in GEOS, that makes it EXTREMELY slow
> for any geometries with +2000 points.
>
> I have posted some info on trac about it:
> http://trac.osgeo.org/mapguide/ticket/172
>
> So, the original problem is "fixed", but it opens another problem,
> which may have more to do with GEOS than with the provider.
> I think the related speed problem makes the provider more useless with
> the fix than without.
>
> I can build a new provider, but I don't have the setup for Oracle and
> PostGIS.
>
>
>
> Regards, Kenneth, GEOGRAF A/S
>
>
>
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> Traian Stanev skrev:
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> Hi.
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> I checked in a temporary fix to this problem. I simply warped one of
> the coordinates of the input polygon by 10^-10. This is sufficient to
> make OGR call GEOS to compute the exact intersection. Selection should
> work correctly now in the AJAX viewer.
>
>
>
> I have not posted a compiled DLL yet, so Kenneth feel free to do so, (-:
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> Traian
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> *From:* mapguide-users-bounces at lists.osgeo.org
> <mailto:mapguide-users-bounces at lists.osgeo.org>
> [mailto:mapguide-users-bounces at lists.osgeo.org] *On Behalf Of *Traian
> Stanev
> *Sent:* Thursday, June 07, 2007 3:46 PM
> *To:* MapGuide Users Mail List; MapGuide Users Mail List
> *Subject:* RE: [mapguide-users] OGR / GEOS selection problem
>
>
>
> Hi Kenneth,
>
>
>
> Thanks for tracking this down. I would try to fix this by bypassing
> Geos. FDO has utility code that can check for an intersection. We
> could take the BBOX result and pass that through a real intersection
> check on the provider side. This way the intersection check would be
> performed only on geometries that are close enough to the query
> polygon so the overhead should not be too bad.
>
>
>
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>
> Traian
>
>
>
> -----Original Message-----
> *From:* mapguide-users-bounces at lists.osgeo.org
> <mailto:mapguide-users-bounces at lists.osgeo.org> on behalf
> of Kenneth, GEOGRAF A/S
> *Sent:* Thu 6/7/2007 2:54 AM
> *To:* MapGuide Users Mail List
> *Cc:*
> *Subject:* [mapguide-users] OGR / GEOS selection problem
>
> Maciej previously reported problems with the OGR provider using
> PostGIS.
>
> The problem is with the OGR provider.
> Se the Trac ticket for details:
> http://trac.osgeo.org/mapguide/ticket/172
>
> I have posted some follow up on the issue, but in hope someone knows a
> lot about GEOS, I'm also posting it here:
>
>
> I have been examining the problem, using a custom build of the OGR
> provider. It is true that without GEOS support in OGR, the Intersect
> only does a BBOX check.
>
> However, merely enabling GEOS will not work, as the viewer sends a
> square that is orthogonal to the axes (like a BBOX). The GEOS library
> will interpret this as another BBOX, and only perform the BBOX check
> anyway.
>
> When I change the polgyon sent from the viewer to a triangle, it takes
> 22 seconds to calculate the Intersects result with a polygon with 8000
> linesegments. I have a 2+ GHz machine.
>
> It seems that GEOS always builds a full intersection matrix, before
> returning the result. This is obviously not optimal for a simple hit
> test. Even with this knowledge, I still don't see how it can take 22
> seconds to calculate 8000 * 3 intersections.
>
> Can someone explain this, or how to fix it?
>
>
>
> --
> Regards, Kenneth, GEOGRAF A/S
>
>
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