[mapserver-users] PHP mapscript $shape->buffer() takes a longtime

[Guillaume Sueur]

Distance maybe ? 

Guillaume

Le mercredi 18 novembre 2009 à 09:27 -0500, Worth Lutz a écrit :
> I'm learning a lot here.
> 
> I now understand how to get the buffered geometry quickly.
> 
> I am using the buffered geometry to use PHP mapscript to select parcel
> intersecting the buffered geometry.
> 
> $layer->queryByShape($bufferedShape);
> 
> Are you telling me that there is a better/faster way to do this?
> 
> 
> 
> -----Original Message-----
> From: mapserver-users-bounces at lists.osgeo.org
> [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Ludwig
> Kniprath
> Sent: Wednesday, November 18, 2009 3:01 AM
> To: mapserver-users at lists.osgeo.org
> Subject: Re: [mapserver-users] PHP mapscript $shape->buffer() takes a
> longtime
> 
> We had the same problem. In deed the buffer-algorithm is very expensive,
> especially with large polygons and a large buffer-radius. If you use
> Postgis, you can simplify the Polygon with ST_Simplify or
> ST_SimplifyPreserveTopology in dependency from scale and buffer-radius, this
> will make the buffer-process much faster without significant loss of
> quality. You can do this on runtime on your original data with dynamic
> PostGIS-queries. If you don't use PostGis, you have to create simplified
> layers.
> 
> Pseudo-PHP-PostGIS-SQL:
> SELECT ...
> ST_SetSRID(ST_BUFFER(ST_SIMPLIFY($geometery_field,$simplify_tolerance),$buff
> er_radius, $number_of_segments),$srid)::geometry ...FROM...
> 
> And don't use the buffered polygon for geo-queries, there are faster ways in
> PostGIS and Mapserver.
> 
> Regards
> Ludwig Kniprath 
> 
> >
> >I'm trying to buffer a shape returned from a point query on a polygon layer
> >of parcels.
> >
> > 
> >
> >When I try to use:
> >
> > 
> >
> >$bufferedShape = $shape->buffer(200);
> >
> > 
> >
> >I get back a fatal error: Maximum execution time of 30 seconds exceeded.
> >
> >I know that this is a php error message and that I could increase the
> >allowable execution time.
> >
> > 
> >
> >If I use a buffer distance of 175 I get results.
> >
> > 
> >
> >Should it take such a long time to but a buffer around this parcel?  It is
> a
> >large parcel with one corner being a long curve like a quarter of a circle
> >and another section on one side being a half circle.
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