[mapguide-users] OGR / GEOS selection problem
Kenneth, GEOGRAF A/S
ks at geograf.dk
Tue Jun 12 18:14:54 EDT 2007
Ok, GDAL 1.4.0 has fixed the problem, by exchanging data in WKB format
instead of WKT.
The WKT parser bug has been fixed in GEOS 3.0.0rc4.
So, your fix works, and the speed problem goes away if I update either
GDAL or GEOS.
So much for not checking for a new version before exploring the problem.
Btw, GDAL 1.4.1 is out.
How do you compile with PostGIS support? I can't find the libpqdll.lib
file anywhere....
Regards, Kenneth, GEOGRAF A/S
Traian Stanev skrev:
>
>
>
> 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
>
>
>
>
> Traian Stanev skrev:
>
>
>
> 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.
>
>
>
>
>
> Traian
>
>
>
>
>
>
>
> *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
>
>
>
>
> Traian Stanev skrev:
>
>
>
> Hi.
>
>
>
> 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
>
>
>
>
>
> *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.
>
>
>
>
>
> 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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