[mapserver-users] Re: Hiding overviews

[Eichner, Andreas - SID-NLK]

Hmm, seems my description wasn't clear enough, so I'll try to precise...

For a layer with raster data I created external overviews. To make use
of them I copied the LAYER portion of the map file, changed the
TILEINDEX statement to point to the index of the appropriate overview,
set MINSCALE/MAXSCALE to form a continues range and added a GROUP
statement to all of them to form a single layer again as it was before
without the overviews added. Now I can take a WMS client, enable or
disable the layer group which collects the detail layer and all of it's
overviews which kick in if you increase the scale.

So instead of having a single layer consisting of huge tiled which have
all to be touched and scaled down for a request at large scales I now
have a group consisting of several layers where only one is active at
each scale. Doing so was a suggestion from the raster data (optimizing)
howto and they called this solution "external overviews".

So if I have a layer "raster" (scale 10...5000000) I want to split it
into "detail" (scale 10...1000) and "overview" (scale 1000...5000000)
and put both in a _group_ "raster" for example. Now you can go and
request the layer "raster" as before and what you get depends on the
chosen scale and is either "detail" below 1000 or "overview" above 1000.

The problem is that you can explicitly request the layer "detail", but
if you are above 1000 you will see... Absolutely nothing. Same with the
"overview" layer below 1000. This is because those layers have a name
which enables them to be requested in a WMS "GetMap" request. If they
wouldn't you could only request the named group layer "raster". So I
thought it could be done by ommitting the "wms_name" part of the
METADATA but if you do and issue a "GetCapabilities" request you will
see that MapServer outputs a warning about the missing mandatory name
attribute and inserts the layer name from the NAME attribute of the map
file.

We have a WMS client which displays nested named layers as folders. The
result isn't user friendly... So I wondered if there's a way to hide
those external overviews from the user since the only thing he can
decide is either to display the hole group (which ever layer may be
affected) or none of those layers at all.

Hope I could make the situation a little bit clearer. I believe it's
only a little thing I miss but there are too much trees in the wood...