[MapServer-users] WMS requests over the antimeridian : inconsistent responses, depending on east or west side

[Philippe Ghesquiere]

Hi Seth,

Thanks for your answer.
I just created a new issue:
https://github.com/MapServer/MapServer/issues/7357

I think this new issue is related to #7212 and #5162

Philippe

On Sun, Oct 5, 2025 at 10:07 AM Seth G <sethg at geographika.co.uk> wrote:

> Hi Philippe,
>
> I'd agree it seems strange this isn't consistent. There is a lot of code
> in the MapServer codebase to handle data crossing the antemeridian, so I
> guess there is an oversight somewhere (and fixing it is likely to be
> tricky). I think this should be added as an issue, with the examples you
> provided.
>
> Seth
>
> --
> web:https://geographika.net & https://mapserverstudio.net
> mastodon: @geographika at mastodon.social
>
> On Fri, Sep 19, 2025, at 4:13 PM, Philippe Ghesquiere via MapServer-users
> wrote:
>
> Dear all,
>
> I noticed a weird behaviour with a WMS request based on EPSG:4326, when
> the BBOX exeeds the [-180 ; +180] longitude intervalle.
> We bump into this problem when we try to display images over the
> antimeridian line.
>
> I could observe this problem with the "MapServer Demonstration Server".
>
>
> *Observed*Mapserver response is not consistent whether the BBOX overlaps
> eastward or westward :
> 1) Westward
> BBOX=-90,-200,90,100
> The image is clipped on both east and west sides, that is in the [-180° ;
> +100°] longitude intervalle.
> On the west side, pixels in the [-200° ; -180°] longitude intervalle are
> transparent.
>
> The complete request URL is :
>
> https://demo.mapserver.org/cgi-bin/wms?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=-90,-200,90,100&CRS=EPSG:4326&WIDTH=953&HEIGHT=480&LAYERS=bluemarble&STYLES=&FORMAT=image/png&TRANSPARENT=true&STYLES=
>
> 2) Eastward
> BBOX=-90,-100,90,200
> The image is clipped on the west side, which is OK.
> On the east side, pixels in the [+180°; +200°] longitude intervalle are
> not correct.
>
> The complete request URL is :
>
> https://demo.mapserver.org/cgi-bin/wms?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=-90,-100,90,200&CRS=EPSG:4326&WIDTH=953&HEIGHT=480&LAYERS=bluemarble&STYLES=&FORMAT=image/png&TRANSPARENT=true&STYLES=
>
>
>
> *Expected*At least, I would expect to have the same behaviour on both
> sides of the antimeridian.
>
> Furthermore, couldn't we get the "repeated world" on the [-200° ; -180°]
> (respectively [+180° ; +200°]) longitude intervalle ?
>
> Thanks for your help
> Philippe
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