optimization

[percy]

One of the tricks I've used to get maps to render quickly at very zoomed 
out levels is to generate simplified versions of my shapefiles, and then 
use maxscale/minscale  settings at the layer level to turn on/off 
simplified/detailed versions as the user zooms in.

PostGIS is nice for this, a simple call like this will generate a 
simplified (one vertex every 1000 map units, feet in this case) shapefile:
pgsql2shp -f simplegeotech {your connection info here}"select 
simplify(the_geom, 1000) as the_geom, lith_gen_u from geotech"
The quotes around the SQL statement are required!

You can see this in action at this site: 
http://geospatial.research.pdx.edu/ogdc/
Notice when you are zoomed out to the entire state if you look REALLY 
close you can see sharp corners like stained glass. This is pulling from 
a database of over 70,000 polygons, and this one trick took me from load 
times in the 30-40 second range down to 4 seconds.

Hope this helps,
Percy

boice tomlin wrote:
> Hello users,
>
> The map located here;
>
> http://gisinventory.net/status_maps.html
>
> takes a while to load.  At least at the national view where there is a 
> lot of area to render.
>
> I am looking for alternative ways to generate the map that will 
> significantly improve performance.
>
> Currently I am using php and looping through data and turning on 
> layers as I go.  The PHP part is lightning fast.  But after I get the 
> map ready mapserver takes several seconds to generate it.
>
> I'm curious about alternative ways to handle this problem and wonder 
> if anyone had comments on any of them.
>
> 1) modifying the shape files in some way so the layer information is 
> in those files.
> 2) using a db such as postgres with postgis.
>
-- 
David Percy
Geospatial Data Manager
Geology Department
Portland State University
http://gisgeek.pdx.edu
503-725-3373