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

[BenH]

I have tried some tests of this.
A simple view, outputting the geometry with ST_Transform, is not
performant at all - the transform breaks the spatial index and it's a
large dataset.
I assume that would still be an issue with a materialized view.
So I think the only PostGIS option would be to create a full copy of the
geometry with its own index. I've tested this, so it is a fall back
option - but it's a lot of data duplication and the Mapserver transform
is really quick.
Thanks

On 06/09/2021 13:38, Mike Saunt wrote:
> 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


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Re: [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,  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 This server is long out of date and we have a new one running 20.02, with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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[mapserver-users] MapServer 7.4.3 - Poor projection from British National Grid (EPSG 27700) to WebMercator (EPSG 3857)

[mapserver]

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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