[MapServer-users] Changing opacity of one layer in a multilayer WMS request URL with MapServer 8

[Steve Lime]

Hi Matthew: That functionality was indeed removed as part of 8.0. I kind of
expect that we might build back something for more limited use cases if
necessary, Does SLD support opacity/transparency?

--Steve


On Tue, Feb 21, 2023 at 10:52 AM Matthew Graber <grabermtw at gmail.com> wrote:

> Hello all!
>
> With MapServer 8, I'm wondering what the proper way to change the opacity
> of a single layer in a multilayer WMS request is.
>
> For example, the following URL excerpt shows the old way of accomplishing
> this that worked while using MapServer 7:
>
>
> SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&LAYERS=test_a,test_b&map.layer[test_b]=OPACITY+50
>
> My understanding is that this would have the same effect as adding
> "OPACITY 50" to the test_b layer in the mapfile. The mapfile containing
> test_a and test_b did not have OPACITY included when they were written.
> Obviously, this no longer works with MapServer 8, and now that request has
> the same results as omitting the "&map.layer[test_b]=OPACITY+50" portion
> entirely.
>
> Based on https://mapserver.org/fr/MIGRATION_GUIDE.html, I see that
> OPACITY now belongs inside a COMPOSITE object. I tried the following
> modifications to the request URL:
>
>
> SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&LAYERS=test_a,test_b&map.layer[test_b].composite=OPACITY+50
>
> SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&LAYERS=test_a,test_b&map.layer[test_b].composite[0]=OPACITY+50
>
> I also tried this both with the mapfile left as-is, and with an empty
> COMPOSITE object being included in each layer object, and each time I got
> the same unsuccessful result as before.
>
> Is there a way to accomplish this in MapServer 8?
>
> Also, does this map.layer[layername]=... syntax still work in MapServer 8?
> The documentation at
> https://mapserver.org/cgi/controls.html#using-mapserver-version-8
> suggests it might no longer work for MapServer 8 (based on the heading
> "Using MapServer version < 8"), but the documentation at
> https://mapserver.org/pdf/MapServer.pdf shows the same examples with the
> heading "Using MapServer version <= 8" on page 1065 of the PDF, so I'm
> unsure if this is still intended to work in MapServer 8.
>
> Thank you,
> Matt
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