SimpleMapServer 'virtual' layers configuration
Virtual layers are layers which doesn't exists, it's just a list or redirection
to various existing layers.
This allow to create layers with a pyramidal structure of LOD, each LOD having
a different number of tiles.
It is also possible to create layers which display completly different data
depending on the zoom factor.
For exemple let say that we have 3 real layers:
- earth1 at low resolution in one small data file.
- earth2 at medium resolution in 4 files.
- earth3 at high resolution in 200 files.
--> we create a virtual layer 'earth' which point to layer earth1 at low
resolution, then earth1, then earth2 at highest resolution.
When the server get a request, it check if the requested layer is virtual, if
so, it look at the requested image resolution, and forward the request to the
layer matching this resolution. The resolution is defined as a range, in data-unit/pixel.
The range property starts with the BIGGEST value, then a space and the SMALLEST
value. If the request match no defined range, the default layer is used.
The list of virtual layers is defined in a property file called 'virtualLayers.props'
which is in the webapp direcory (folder where there is by default the mapServer.props
file).
Here is an exemple of setting:
# this setting file will define 'virtual' layers
# - a virtual layer is an alias to one or several existing layers
# - a virtual layer may have several redirection to various layers, each redirection
is defined by a resolution 'range'
# - the range is expressed in data-file-unit/pixel. '+' is for infinity, '-'
is for minus infinity
# - a virtual layer can be 'visibl'e or not in the capabilities
# - if no range match the requested resolution, the 'default' existing layer
is used
# - the description field will be used in the capabilities (instead of the default
layer one)
# - one redirection is defined by 2 consecutive lines: layer= then range=.
start_virtual_layer=toto
description=toto layer, virtual of Visible 3
visible=true
default=Visible3
layer=Visible2
range=.2 .002
layer=Default
range=.002 -
end_virtual_layer
start_virtual_layer=titi
description=titi layer, virtual of Visible 2
visible=true
default=Visible2
layer=Visible2
range=.2 -
end_virtual_layer
gilles.lavaux <at> serco <dot> com