[Gdal-dev] WMS and LAYERS= vs. STATUS Behaviour

[Frank Warmerdam]

Daniel and others,

I have been experimenting a bit with the Gaia WMS viewer
(http://www.nukegold.com/downloads.htm) a bit against MapServer, and
found something that surprised me.

It seems that a layer with STATUS DEFAULT will be returned in a GetMap
request against MapServer regardless of whether the layer is in the
layers list or not.  Is this the expected behaviour?

I have a WMS server (from CVS) servering 3 layers, all of which have
STATUS DEFAULT.  Even if I ask for just one of them, it would appear I
get all 3.

I would have hoped MapServer would have:
  o returned only the requested layers if there is a LAYERS= parameter
    in the WMS GetMap request.
  o Returned only STATUS DEFAULT layers if there was no LAYERS= parameter
    in the WMS GetMap request.

If things are behaving as intended, then I think the WMS Server HOWTO
should mention this gotcha.

If things are not working as intended, it would appear the following code
in mapwms.c needs some alterations:

     // getMap parameters
     if (strcasecmp(names[i], "LAYERS") == 0)
     {
       int  j, k, iLayer;

       layers = split(values[i], ',', &numlayers);
       if (layers==NULL || numlayers < 1) {
         msSetError(MS_WMSERR, "At least one layer name required in LAYERS.",
                    "msWMSLoadGetMapParams()");
         return msWMSException(map, wmtver, NULL);
       }


       for (iLayer=0; iLayer < map->numlayers; iLayer++)
           map->layerorder[iLayer] = iLayer;

       for(j=0; j<map->numlayers; j++)
       {
         // Keep only layers with status=DEFAULT by default
         // Layer with status DEFAULT is drawn first.
         if (map->layers[j].status != MS_DEFAULT)
            map->layers[j].status = MS_OFF;
         else
            map->layerorder[nLayerOrder++] = j;
       }

       for (k=0; k<numlayers; k++)
       {
           layerfound = 0;
           for (j=0; j<map->numlayers; j++)
           {
               // Turn on selected layers only.
               if ((map->layers[j].name &&
                    strcasecmp(map->layers[j].name, layers[k]) == 0) ||
                   (map->name && strcasecmp(map->name, layers[k]) == 0) ||
                   (map->layers[j].group && strcasecmp(map->layers[j].group, layers[k]) == 0))
               {
                   map->layers[j].status = MS_ON;
                   map->layerorder[nLayerOrder++] = j;
                   validlayers++;
                   layerfound = 1;
               }
           }
           if (layerfound == 0)
             invalidlayers++;

       }

       // set all layers with status off at end of array
       for (j=0; j<map->numlayers; j++)
       {
          if (map->layers[j].status == MS_OFF)
            map->layerorder[nLayerOrder++] = j;
       }

       msFreeCharArray(layers, numlayers);
     }

I can provide a demonstration of the problem if required.

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent