Implementing Scale-Dependent Styles in a WMS Server

[Jim Klassen]

If I understand your setup, you are in charge of two mapserver installs,
one being a WMS server and another acting as a WMS client.

I don't know what this will do to the getCapabilities response (and it
doesn't matter if Mapserver is your only client), but you could in the
WMS servers map file try adding a GROUP 'mygroup' statement to each of
your layers, thus assigning each of the layers to the same group. Each
of the layers can then be setup with the correct styles and min/max
scales. 

Then try calling the WMS service and ask it for the 'mygroup' layer.

We do something similar here internally with our aerial orthos, except
we have one mapfile per logical layer and just set status=default in all
of the layers in the mapfile so they will always be rendered, no matter
which one the client chooses. (The min/max scales are setup so only one
layer from the mapfile will be active at any given scale.) 

>>> Bill Thoen <bthoen at GISNET.COM> 07/26/07 9:41 AM >>>
I'm starting to build a MapServer WMS server that will provide national 
street layers to my MapServer client but I have some questions about how

to approach the problem of serving alternate layers designed for 
different scales and same layers with different styles depending on the 
scale. For example, I've got a US Interstates layer that has been 
thinned so that it is appropriate for scales smaller than 1:10,000,000, 
and I've got another one that I'd use at larger scales (but from 
1:10,000,000 to 1:5,000,000 I want to use one style and for scales 
between 1:5,000,000 and 1:1,000,000 I want to use another style on this 
layer). Then I've got some MapInfo seamless road layers that have the 
highest detail that I'd use at the largest scales, but for these too, I 
have three different styles depending on the display scale.

Can a MapServer WMS server support this sort of thing or should I load 
each layer as needed and style it in the WMS client MAP file? I know how

to do the latter, but it would be much more convenient to make one call 
to a WMS and get all the appropriate layers rendered with the desired 
styles in one LAYER call in my client MAP files. I've read the how-tos 
for WMS client and server, and glanced at the article about SLD's (but 
haven't understood that very well yet) but so far I haven't seen this 
issue addressed specifically.  Does anyone have any suggestions about 
how to do this, or can you point me to any documentation I should read?

TIA,
- Bill Thoen