[MapServer-users] Use SCALETOKEN in FILTER?

[Jesper Kempe]

Thanks Seth!
That was a creative workaround. Will use that for now.

But I will also create an issue for this bug.

Jesper

Den tors 13 feb. 2025 kl 12:53 skrev Seth G <sethg at geographika.co.uk>:

> Hi Jesper,
>
> As a workaround (unless this was the intended design), you can use the
> following approach:
>
>         SCALETOKEN
>             NAME "%ne_scalerank%"
>             VALUES
>                 "0" "([scalerank] < 10)"
>                 "1000" "([scalerank] < 8)"
>                 "10000000" "([scalerank] < 5)"
>             END
>         END
>         FILTER "%ne_scalerank%"
>
> Seth
>
>
> --
> web:https://geographika.net & https://mapserverstudio.net
> mastodon: @geographika at mastodon.social
>
> On Thu, Feb 13, 2025, at 12:31 PM, Seth G via MapServer-users wrote:
>
> Hi Jesper,
>
> This looks like a bug - it should work as you expect it to.
> Could you log an issue at https://github.com/MapServer/MapServer/issues ?
>
> Seth
>
> --
> web:https://geographika.net & https://mapserverstudio.net
> mastodon: @geographika at mastodon.social
>
> On Wed, Feb 12, 2025, at 3:13 PM, Jesper Kempe via MapServer-users wrote:
>
> Hi
>
> I am trying to show different levels of details based on zoom level in a
> map based on Natural earth 10m data (ne_10m_lakes.zip from
> https://www.naturalearthdata.com/downloads/10m-physical-vectors/) using
> the attribute scalerank in the shape file.
>
> My plan was to use SCALETOKEN to replace the value in a FILTER with the
> current max scalerank to use.
> But I cant get it to work. Nothing is shown in the map.
>
> Should it be possible to use a scaletoken in a filter expresssion?
>
> Looking at https://mapserver.org/development/rfc/ms-rfc-86.html#discussion
> it looks like it at least was planned to work?
>
> Now I get errors like this in the log file:
>
> [Wed Feb 12 13:50:20 2025].23938 replacing scaletoken (%ne_scalerank%)
> with (5) in layer->filter (ne_10m_lakes) for scale=221471921.250000
> [Wed Feb 12 13:50:20 2025].24460 msEvalExpression(): General error
> message. Cannot evaluate expression, no item index defined.
> [Wed Feb 12 13:50:20 2025].24474 msEvalExpression(): General error
> message. Cannot evaluate expression, no item index defined.
> [Wed Feb 12 13:50:20 2025].24482 msEvalExpression(): General error
> message. Cannot evaluate expression, no item index defined.
>
> Using this mapfile:
> MAP
>     CONFIG "MS_ERRORFILE" "ms_error.txt"
>
>     STATUS ON
>
>     PROJECTION
>         "init=epsg:4326"
>     END
>
>     EXTENT -180 -90 180 90
>
>     WEB
>         METADATA
>             "wms_title"           "WMS Demo Server"
>             "wms_srs"             "EPSG:4326"
>             "wms_enable_request"  "*"
>         END
>     END
>
>     LAYER
>         DEBUG 5
>         NAME 'ne_10m_lakes'
>
>         TYPE POLYGON
>         PROJECTION
>             "init=epsg:4326"
>         END
>         EXTENT -180 -90 180 90
>         DATA "ne_10m_lakes.shp"
>
>         SCALETOKEN
>             NAME "%ne_scalerank%"
>             VALUES
>                 "0" "10"
>                 "1000" "8"
>                 "10000000" "5"
>             END # VALUES
>         END # SCALETOKEN
>
>         FILTER ([scalerank] < %ne_scalerank% )
>
>         CLASS
>             STYLE
>                 OUTLINECOLOR "#647078"
>                 WIDTH 1
>                 COLOR "#EBEEF0"
>             END
>         END
>
>     END
>
> END
>
> For this request
>
> https://myserver/wms?&service=WMS&request=GetMap&layers=ne_10m_lakes&styles=&format=image%2Fpng&transparent=false&version=1.1.1&map=ne_10m_lakes.map&height=512&width=512&srs=EPSG%3A4326&bbox=-180,-90,180,90
>
> Worth noting is if I replace FILTER ([scalerank] < %ne_scalerank% ) with
> FILTER ([scalerank] < 5 ) in the mapfile it works fine.
>
> Anyone with thoughts or ideas on how this can be solved?
>
> I am on Mapserver 7.6.4.
>
> Thanks,
> Jesper
>
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