Single WMS from single mapfile with several rasters in MapServer - layer

Question

I have several rasters in a single mapfile, I put them as layers like here:
LAYER
NAME "Layer 1"
GROUP "All Layers"
TYPE RASTER
STATUS ON
DATA "layer1.png"
PROJECTION
"init=epsg:4326"
END
METADATA
"wms_title" "Layer 1"
"wms_srs" "EPSG:4326"
"wms_group_title" "All layers"
"wms_abstract" "No abstract"
"wms_server_version" "1.1.1"
"wms_format" "image/png"
"wms_include_items" "all"
"gml_include_items" "all"
"gml_geom_type" "raster"
END
END
LAYER
NAME "Layer 2"
GROUP "All Layers"
TYPE RASTER
STATUS ON
DATA "layer2.png"
PROJECTION
"init=epsg:4326"
END
METADATA
"wms_title" "Layer 2"
"wms_srs" "EPSG:4326"
"wms_group_title" "All layers"
"wms_abstract" "No abstract"
"wms_server_version" "1.1.1"
"wms_format" "image/png"
"wms_include_items" "all"
"gml_include_items" "all"
"gml_geom_type" "raster"
END
END
LAYER
NAME "Layer 3"
GROUP "All Layers"
TYPE RASTER
STATUS ON
DATA "layer3.png"
PROJECTION
"init=epsg:4326"
END
METADATA
"wms_title" "Layer 3"
"wms_srs" "EPSG:4326"
"wms_group_title" "All layers"
"wms_abstract" "No abstract"
"wms_server_version" "1.1.1"
"wms_format" "image/png"
"wms_include_items" "all"
"gml_include_items" "all"
"gml_geom_type" "raster"
END
END
The problem is that I want to have a single WMS layer (named as in GroupTitle) as output from this mapfile (because it is only one mapfile), instead I have four WMS layers (three coming from each LAYER and one from the GROUP LAYER).
How can I achieve what I want? I use Mapserver 6.4.1 in OL 2.11.
Any ideas are welcomed, thanks in advance,

Answer 1

You can just use the GROUP element:
LAYER
NAME "layer1"
GROUP "both_layers"
STATUS OFF
TYPE RASTER
DATA "layer1.tif"
END
LAYER
NAME "layer2"
GROUP "both_layers"
STATUS OFF
TYPE RASTER
DATA "layer2.tif"
END
Then you reference "both_layers" in your WMS requests.

Answer 2

It appears that a Union Layer would do what you're asking. I haven't tried it myself. From the documentation linked above:
LAYER
NAME "union-layer"
TYPE POINT
STATUS DEFAULT
CONNECTIONTYPE UNION
CONNECTION "layer1,layer2,layer3" # reference to the source layers
PROCESSING "ITEMS=itemname1,itemname2,itemname3"
...
END
LAYER
NAME "layer1"
TYPE POINT
STATUS OFF
CONNECTIONTYPE OGR
CONNECTION ...
...
END

Answer 3

I believe that what you are looking for is the TILEINDEX approach that was introduced in 6.4.
To quote the reference:
When handling very large raster layers it is often convenient, and higher performance to split the raster image into a number of smaller images. Each file is a tile of the larger raster mosaic available for display. The list of files forming a layer can be stored in a shapefile with polygons representing the footprint of each file, and the name of the files.
See Rasters and Tile Indexing