[mapguide-users] WMS Polygon clipping problems

[Traian Stanev]

One big difference is that GETTILE uses a different labeling algorithm
which attempts to avoid problems with labels spanning multiple tiles.
You will likely get labeling artifacts if you are tiling WMS requests
for data that is labeled. How important is that in your case?
 
The tile size in MG is currently set to 300x300 pixels. We chose a
bigger size because labeling would behave better the bigger tiles are,
there would be less http requests made to the server, and the set-up
time overhead to draw a map image is usually a lot longer than the
actual time it takes to draw the geometry, so by having bigger tiles
that overhead is distributed across more features.
 
However, I see that for overlay with Google Maps, the ability to set
tile size down to 256 may be useful, especially if you expect that
caching the tiles would give a significant performance boost.
 
Traian
 

  _____  

From: Andy Morsell [mailto:amorsell at spatialgis.com] 
Sent: Monday, May 22, 2006 11:35 PM
To: users at mapguide.osgeo.org
Subject: RE: [mapguide-users] WMS Polygon clipping problems


Regarding people making tiles on their own: with Google Maps, if one
wants to add their own layers, they have to use the GTileLayer
interface.  By definition the Google Maps API automatically makes one
call to the layer source per 256x256 pixel tile.  I don't think there is
a way to override this and instead use a visible extent overlay.  It
does look like you might be able to change the tile size, but you are
stuck with tiles regardless.  So, if using MGOS as the source, we have
to use one WMS call per tile or possibly use the GETTILEIMAGE operation.
I have not experimented much with the latter and would rather stick with
WMS calls anyway for conformity.
 

Andy 


  _____  

From: Traian Stanev [mailto:traian.stanev at autodesk.com] 
Sent: Monday, May 22, 2006 5:33 PM
To: users at mapguide.osgeo.org; users at mapguide.osgeo.org
Subject: RE: [mapguide-users] WMS Polygon clipping problems




OK. I'll check what can be done. It's really a one line change when it
comes down to it, but I'm not sure what other code calls that function
that might be affected. Since people seem to make tiles on their own,
the change is probably worth the performance loss this change entails...

Traian


-----Original Message-----
From:   Andy Morsell [mailto:amorsell at spatialgis.com]
Sent:   Mon 5/22/2006 8:22 PM
To:     users at mapguide.osgeo.org
Cc:    
Subject:        RE: [mapguide-users] WMS Polygon clipping problems

Traian,
This is specific to WMS.  The screenshot is from Google Maps where the
tiles
are individual WMS calls to MapGuide Open Source.

Thanks.


Andy


  _____ 

From: Traian Stanev [mailto:traian.stanev at autodesk.com]
Sent: Monday, May 22, 2006 4:58 PM
To: users at mapguide.osgeo.org; users at mapguide.osgeo.org
Subject: RE: [mapguide-users] WMS Polygon clipping problems




This is strange. For WMS I can see how it would happen. However, for a
regular  tiled map, we turn off polygon clipping to avoid this. Are you
using a regular tiled map or is this screenshot from WMS?

Traian


-----Original Message-----
From:   Andy Morsell [mailto:amorsell at spatialgis.com]
Sent:   Mon 5/22/2006 6:28 PM
To:     users at mapguide.osgeo.org
Cc:   
Subject:        [mapguide-users] WMS Polygon clipping problems

There is an older thread on this topic at:
https://mapguide.osgeo.org/servlets/ReadMsg?list=users
<https://mapguide.osgeo.org/servlets/ReadMsg?list=users&msgNo=488>
&msgNo=488

I am experiencing this problem as well when working in a tiled
environment.
This screenshot illustrates the problem where there are several large
polygons that have boundaries drawn at the clipping edges.  I did not
see an
issue in Project Tracker about this and just wanted to re-raise the
issue to
ensure that it is addressed soon.

Thank you.

Andy Morsell, P.E.
Spatial Integrators, Inc.
http://www.SpatialGIS.com









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