[mapserver-users] MapServer 7.4.3 - Poor projection from British National Grid (EPSG 27700) to WebMercator (EPSG 3857)

[Mike Saunt]

Ben

Have you considered using PostGIS to do the transformation instead?  Also,
depending on the amount of data you could set up some material views
building transformed data or similar which may make it more responsive, if
that is needed.

All the best
Mike


On Mon, 6 Sept 2021 at 11:52, <mapserver at brainspeedjelly.co.uk> wrote:

> Reposted from
> https://gis.stackexchange.com/questions/410874/mapserver-7-4-3-poor-projection-from-british-national-grid-epsg-27700-to-web
>
> We have PostGIS data in BNG and are displaying it over Google satellite
> imagery.
>
> This worked fine previously - using a Ubuntu server running 18.04, with
> MapServer 7.0.7, GDAL 2.2.3, proj 4.9.3.
>
> This server is long out of date and we have a new one running 20.02, with
> MapServer 7.4.3, GDAL 3.0.4 and proj 6.3.1. However this is projecting the
> BNG layers incorrectly (~200m ESE).
>
> This appears to be similar to the issue reported at
> https://github.com/OSGeo/gdal/issues/3695 although that claims the
> problem only arose after proj 7.2.1
>
> I have installed the updated transform OSTN15_NTv2_OSGBtoETRS.gsb but this
> had no effect.
>
> Is there a way to update the transforms used by MapServer or get MapServer
> to pass the transformation to PostGIS ?
>
> Thanks
>
> Ben
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