Hi,
I don’t know why Tom asks this but I tried to imagine some use cases:
-
Aerial image/satellite image provided sells license for some limited use and something like parcel data layer or pipe network layer could be used as sort of watermark if layers must be used together.
-
Same as before, but the other layer could be a mask layer
-
For security reasons route layer could not be used without showing also the layer for sea marks and hazardous areas.
MapServer has couple of mechanisms for doing something like that: mask layer and keyword REQUIRES / LABELREQUIRES
http://mapserver.org/development/rfc/ms-rfc-79.html
http://mapserver.org/mapfile/layer.html#labelrequires
The REQUIRES keyword is not very well documented but I remember that have used it sometimes for making “copyright text 1” appear if topographic layer is required from WMS and “copyright text 2” if aerial images are requested. When implemented this way I think it complies with the WMS standard. It is possible to request any combination of layers, but if you request &layers=secured you will get the same result as if the request was &layers=secured,mask. Rendering secured+mask always together can be interpreted as default style for the “secured” layer.
-Jukka Rahkonen-
···
Andrea Aime wrote:
On Thu, Oct 9, 2014 at 11:02 AM, Tom Chadwin <tom.chadwin@…3373…> wrote:
Is it possible to allow certain layers to be requested only when other layers
are requested with it?
In general terms, that would break the WMS contract, which allows any combination of the exposed layers.
Well, of course unless you do not expose the layer in question (make it non advertised),
and eventually lump it into opaque layer groups… at this point the clients will not see it, but it will
still be available as part of the layer groups
If you don’t mind me asking, why do you need the layer to only show up along with other layers?
Cheers
Andrea
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