[OpenLayers-Users] trouble with WFS and Mapserver - Performance Indicators

[Burgholzer,Robert]

Thanks for all the help on this one, with a hybrid approach, WMS for
window dressing, WFS for interaction, and a little simplify()'ing, my
performance has increased dramatically.

Just for posterity, the following are some performance indicators for
this situation.  I have chosen to use the length of the WKT string that
the shapes translate to from a postGIS "asText" call, as a surrogate for
number of points (this seems easier than trying to get the number of
points from a multiploygon):
- My initial data set contained 3 MULTIPLOYGONS, WKT string lengths
between 62,000 and 85,000
- Data were processed with the postGIS function, simplify, with a
tolerance of 0.0025 decimal degrees (trial and error led me to that, no
loss of shape integrity)
- Shapes simplified to WKT strings of length between 2,100 to 2,800
- Loading times went from about 2 minutes (with several "script not
responding" error messages) down to less than 10 seconds
- Client/Server Machine is a workstation, WinXP SP2, 2.8 GHz CPU, 1.5 GB
RAM, 

So, while this situation is not exactly precise, it sets some overall
bounds, that is, around 7,000 character shape strings will render out in
an acceptable time frame (with map pans excellent, i.e., instantaneous
rendering, and map zooms reasonable, i.e. ~3.0 seconds to redraw),
whereas, on the given system, WKT strings of 200,000 characters was a
non-starter.

r.b.



-----Original Message-----
From: Christopher Schmidt [mailto:crschmidt at metacarta.com] 
Sent: Friday, September 28, 2007 11:42 PM
To: Burgholzer,Robert
Cc: users at openlayers.org
Subject: Re: [OpenLayers-Users] trouble with WFS and Mapserver -
Partially solved

On Fri, Sep 28, 2007 at 03:42:57PM -0400, Burgholzer,Robert wrote:
> Hmm. It seems that every solution finds a new problem.  I managed to
discern my trouble - it had to do with URL location.
> 
>  
> 
> I am testing my application and WFS server all on my local
workstation.  The issue, after straightening out the baseLayer and
projection trouble, came from the location of my script, where I was
using a 172.16. notation to access it, and the location of the WFS
server, which I was calling as "localhost".  Thus, a proxy, or
consistent URL scheme was required.  I initally ran into the trouble
because my script was freezing my browser, and blowing up memory
requirements, so I tried "localhost" as my WFS location, and everything
sped up, but of course, nothing appeared, because I would have needed a
proxy setting.  But, the trouble really stemmed from the fact that my
shapes are too complex, I suppose.  There are 250 shapes in my layer,
and that is choking everything up.  They are relatively complicated
county boundaries.  If I set "maxfeatures: 10" in my request, things go
faster, and the shapes are rendered in about 30 seconds.  However, I
really need to be able to see all of my shapes, and would like response
times to be reasonable.  The WFS url request loads in less than 10
seconds, so, I would not want much more overhead above that.
> 
>  
> 
> Any suggestions?

Off the top of my head:

 * simplify()

or 

 * WMS

Regards,
-- 
Christopher Schmidt
MetaCarta