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
