[mapguide-users] OGR / GEOS selection problem

Tue Jun 12 20:10:48 EDT 2007

OK thanks. I am suffering bandwidth problems (time bandwidth that is) right now, so that's my excuse for taking time fixing OGR provider bugs. The next issue that I am thinking about fixing is the unicode problem with utf8 strings that Maciej reported, unless some worse problem comes in.

Traian

	-----Original Message----- 
	From: mapguide-users-bounces at lists.osgeo.org on behalf of Kenneth, GEOGRAF A/S 
	Sent: Tue 6/12/2007 7:11 PM 
	To: MapGuide Users Mail List 
	Cc: 
	Subject: Re: [mapguide-users] OGR / GEOS selection problem

	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: 

		GDAL 1.4.0, GEOS 2.2.3.

		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] 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, (-:

		Traian

		From: 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 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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