[mapserver-users] WMS Layers and Grouping (FWD)

[Rob Atkinson]

Not such a problem:

If a layer has a <Name> it can be addressed as a layer - and will include all
the sub-layers.

A Layer may have a <Title> but no <Name> - in which case it is not allowed to
be accessed directly, but can be used as a template and also as a grouping
title in legends.

I think this addresses all the issues, and yes - it would be way cool
implement this automatically.

Rob

Daniel Morissette wrote:

> Paul Ramsey wrote:
> >
> > - The WMS Capabilities includes the ability to "nest" layers, such that
> > one could have a description like this:
> >   <Layer>
> >     <Title>Water Features</Title>
> >     <Name>water</Name>
> >     <Layer>
> >       <Title>Rivers</Title>
> >       <Name>rivs</Name>
> >     </Layer>
> >     <Layer>
> >       <Title>Lakes</Title>
> >       <Name>lks</Name>
> >     </Layer>
> >   </Layer>
> >
> >   This would be kind of cool to be able to do. Using the mapserver
> >   'group' idea to implement this is possible. However, I have another
> >   question regarding 'group', and it goes like this:
> >
>
> Agreed, this was already filed as a enhancementt:
>   http://mapserver.gis.umn.edu/bugs/show_bug.cgi?id=12
>
> > - Oftentimes, people will use the mapserver 'group' to provide one
> >   "virtual" layer made out of a whole bunch of scale-dependant layers.
> >   So, you have a group 'roads' which consists of 1:6Million roads
> >   at full extent, 1:250K roads partway in, and 1:20K roads at max
> >   zoom. Right now, mapservers WMS will report all the constituent
> >   layers of this virtual layer in the Capabilities file, like
> >   this:
> >
> >   <Layer>
> >     <Title>roads_6M</Title>
> >   </Layer>
> >   <Layer>
> >     <Title>roads_250K</Title>
> >   </Layer>
> >   <Layer>
> >     <Title>roads_20K</Title>
> >   </Layer>
> >
> >   When really, as a map publisher I would prefer to just expost
> >   the thing as one virtual layer, thusly:
> >
> >   <Layer>
> >     <Name>Roads</Name>
> >   </Layer>
> >
> > So, two different problems, but I do not have a clean solution in my
> > head in terms of mapping file syntax, to allow these kinds of WMS
> > constructions from a map file.
> >
>
> I agree with your suggestion... in this case the group discussed earlier
> would do the trick since it would group under a top-level "Roads" layer
> all the scale-specific Roads layers and would still give access to the
> individual layers.
>
> However I see why you may not want individual layers to be visible.
> There are a few ways that we could handle this:
>
> 1- We could have a "wms_hidden" metadata... if it is set then the layer
> is not visible in the WMS capabilities.  We would have to define how
> this works in combination with the grouping described above.
>
> 2- Right now, if 2 layers have the same name then MapServer's WMS
> interface will try to give them unique names in the capabilities by
> appending a number to the individual layer names (i.e. if your mapfile
> contains 3 layers with name "roads" then the capabilities will return
> roads_1, roads_2, roads_3)
>
> We could modify the interface so that it is legal to have layers with
> identical names, and then only the first one with that name is shown in
> the capabilities, the other ones are automatically hidden.  All layers
> with the same name would be turned on automatically in a getMap request
> if that layer name is requested.
>
> I had to write this quickly...maybe it won't make much sense when you
> read it?  Anyway, if you (and the other users) like one of those options
> then you might want to file a enhancement request in bugzilla.
>
> Best Regards,
> --
> ------------------------------------------------------------
>  Daniel Morissette               morissette at dmsolutions.ca
>  DM Solutions Group              http://www.dmsolutions.ca/
> ------------------------------------------------------------
>   Don't put for tomorrow what you can do today, because if
>       you enjoy it today you can do it again tomorrow.
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