[ka-Map-users] KaMap performance tuning

[Jeff Dege]

In our case, we don't have any filter expressions on the data.  We're
drawing all the streets.  (Or rather, at the zoom levels where we're not
drawing all the streets, we've extracted the streets that we are drawing
to separate, smaller, shapefiles.)

> -----Original Message-----
> From: ka-map-users-bounces at lists.maptools.org 
> [mailto:ka-map-users-bounces at lists.maptools.org] On Behalf Of percy
> Sent: Thursday, May 24, 2007 2:54 PM
> To: ka-map-users at lists.maptools.org
> Subject: [ka-Map-users] KaMap performance tuning
> 
> I recently was able to get an extremely complex geologic data 
> shapefile set to render much faster (after doing all of the 
> other optimizations mentioned by everyone else) by tuning the 
> filter expressions.
> 
> I changed all class expressions from the following statement type
>  CLASS
>   NAME 'Dominant:Clastic sediment;'
>   EXPRESSION ('[LithComp]' eq 'Dominant:Clastic sediment;')
>   STYLE
>    COLOR 255 255 0
>   END #STYLE
>  END #CLASS
> 
> to
> 
>  CLASS
>   NAME 'Dominant:Clastic sediment;'
>   EXPRESSION 'Dominant:Clastic sediment;'
>  
>   STYLE
>    COLOR 255 255 0
> 
>   END #STYLE
>  END #CLASS
> 
> I was stunned at the performance increase this gave me, 
> though it's obvious why it helps so much (in hindsight). The 
> only reason I was using the former EXPRESSION statements was 
> because I had used QGIS or AMEIN to auto-generate the initial 
> mapfile...
> 
> Hope this helps,
> Percy
> 
> 
> 
> Date: Tue, 22 May 2007 19:13:03 -0700
> From: Paul Ramsey <pramsey at refractions.net>
> Subject: Re: [ka-Map-users] KaMap performance tuning
> To: Jeff Dege <jdege at korterra.com>
> Cc: ka-map-users at lists.maptools.org
> Message-ID: <6207F842-AAF6-44EE-8A58-B08C960D4812 at refractions.net>
> Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed
> 
> 10:1 speed advantage for PostGIS is nice and all, but seems 
> unlikely,  
> even to this PostGIS zealot...
> 
> Does your layer have a FILTER on it that uses the attributes? 
> PostGIS  
> does that great, shapefiles do it terribly.
> 
> I would expect on a very large spatial file (your 500MB example) the  
> PostGIS r-tree will be balanced better than the quadtree .qix file,  
> but that should provide incremental advantage, not massive  
> advantage.  One possibility is that you're running out of depth in  
> your quadtree, maybe tree bumping up the depth in your shptree call.
> 
> P
> 
> 
> >   
> >> We'd never had trouble with the performance of shapefiles, 
> until we  
> >> had to deal with one that contained the California streets.    
> >> 500MB .shp file, 600MB .dbf file, and performance with it was dog  
> >> slow.
> >>
> >> We pulled out interstates, highways, and main roads, into 
> separate  
> >> shapefiles, so that we didn't have to touch the streets 
> data until  
> >> we were zoomed in tight, and performance was still dog 
> slow when we  
> >> did.
> >>
> >> We split the streets shapefile into hundreds of separate tiles,  
> >> shptreed each, built a tileindex on the bunch, then shptreed the  
> >> tileindex, and performance was a good bit better, but still not  
> >> acceptable.
> >>
> >> The people I've been talking to have told me that when rendering  
> >> everything, shapefiles are faster, but when rending small subsets  
> >> of the data, PostGIS can be considerably faster.  Particularly if  
> >> you use it's simplify() function to tune the resolution of 
> the data  
> >> returned to the scale of the map.  I've only begun experimenting  
> >> with this, but nothing in my experience so far contradicts this.
> >>
> >> Shp2img, rendering a map with an extent of .04 decimal degrees,  
> >> took 17.198 seconds to render the streets layer using (tiled)  
> >> shapefiles, it took 0.219 seconds to render the streets 
> layer using  
> >> PostGIS.
> >>
> >>     
> -- 
> David Percy
> Geospatial Data Manager
> Geology Department
> Portland State University
> http://gisgeek.pdx.edu
> 503-725-3373
> 
> 
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