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

[Seth G]

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 

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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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