I had the same problem of loading a heavy WFS layer and didn't want to use WMS as an alternate solution because I wanted to change the opacity when over a feature.
The features are polygons. I use mapserver with shapefiles. I wrote a little script using phpmapscript which loads a given shapefile, get each polygon and for a given a scale ( which gives a resolution ) get each point in each polygon and compare the distance between them one by one. If the distance is shorter than the resolution ( i.e. if the two points are in the same pixel ) I skip the second point and check the next one. If not, I add the second point ( it becomes the first ) and go the the next one. The result generates a new shorter shapefile to be used for the given scale. I did that for 5 different scales so in OL I have 5 differents layers that only shows data when they are in their range. I hid them from the layerswitcher, created a dummy layer that interacts for both 5 of them instead. I works great, but I haven't done much yet so I have to do many operations manually ( like, editing the mapfile to add each the new layer... ) I compressed the data even more by changing the (1 point / pixel) by (1 point / 3 pixels). The result gives a shorter file, a faster loading time and gives a smoother image. Cheers, Alexandre G. Allegri wrote: > Mmm, as I was expecting it's not a good solution for polygons. The > simplification removes the little ones, and it's ok, but it returns a > lot of holes along the polygon boundaries, as it doesn't preserve a > topological coherence. I hope the next release of PostGIS will > integrate the topology suite (at the moment in beta version). > > 2008/9/18 G. Allegri <[EMAIL PROTECTED]>: > >> I was doing it right now :-) >> I was blocked by a problem while I was creating a view for the >> simplified geometries. The simplify alone works fine, but with the >> create view statement it returns empty... But this is something for >> the PostGIS ML. >> >> Thanks anyway for sharing the URL. >> >> 2008/9/18 percy <[EMAIL PROTECTED]>: >> >>> I haven't tried this with WFS, but... >>> >>> I display "simplified" geometry when zoomed out with geologic map polygons. >>> >>> I use the PostGIS simplify(the_geom, $vertex_density) command to generate >>> polygons with only one vertex every 500m, for example, when zoomed out past >>> a certain extent. This is served via Mapserver using minscale/maxscale >>> settings at the layer level. >>> >>> You can create different columns of simplified geometries for use at >>> different scales (thegeom_2M, thegeom_500K, etc) in PostGIS. Or you can >>> process the data and spit out different shapefiles for each scale range. >>> >>> Sometimes I can see some artifacts of the simplification, since topology >>> constraints are not part of the process. It has a little "jagginess" like >>> stained glass, but when you zoom in to see what the artifact is, I have >>> substituted the high-res data and it's no longer there! >>> :-) >>> >>> I'm pretty sure this approach will work for what you want to do. You can see >>> a non-openlayers version of this here: http://ogdc.geos.pdx.edu/ >>> >>> Cheers, >>> Percy >>> >>> G. Allegri wrote: >>> >>>> Hi list, >>>> I need to load a heavy GML (the original shapefile is >12 MB), and I >>>> can't make any simplification, beacuse it's composed by little, >>>> needed, polygons. >>>> Has ever been experimented something to do a sort of "pyramids" with >>>> vectorial features? The only solution I can imagine is to produce >>>> various simplifications, and then call different GMLs on the base of >>>> the zoom factor... Well, it isn't a solution, it would be just a >>>> horrible workaround! >>>> >>>> Any idea to share? >>>> _______________________________________________ >>>> Users mailing list >>>> [email protected] >>>> http://openlayers.org/mailman/listinfo/users >>>> >>>> >>> -- >>> David Percy >>> Geospatial Data Manager >>> Geology Department >>> Portland State University >>> http://gisgeek.pdx.edu >>> 503-725-3373 >>> >>> > _______________________________________________ > Users mailing list > [email protected] > http://openlayers.org/mailman/listinfo/users > -- Alexandre Dubé Mapgears www.mapgears.com _______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
