[postgis-users] Using grids transformation method with PostGis

[Francis Markham]

I would also be interested in the answer to this question.  Currently I
export PostGIS data to shapefiles and use ogr2ogr to transform, if a grid
shift is required.  Perhaps the solution to this problem could be documented
on the ST_Transform() page in the PostGIS manual?

Cheers,

Francis

2010/6/9 Luís de Sousa <luis.a.de.sousa at gmail.com>

> Hello everyone,
>
> I'm trying to convert a series of spatial features from one SRS to
> another within PostGIS. Both are local systems for continental
> Portugal, for which a set of grid definition files have been made
> available by the University of Oporto. I downloaded these grid files
> and copied them into /usr/share/proj and /usr/local/share/proj. That
> was enough to get proj to start using them.
>
> The problem is, when invoking the same transformation from PostGis I'm
> getting errors in the range of tenths, sometimes hundreds, of metres.
> It seems like PostGis is failing to use the grid files. In attachment
> goes a log demonstrating the same transformation having different
> results with proj and PostGis.
>
> What am I missing? Is there any extra configuration needed for PostGis
> to use the grid files?
>
> Thank you,
>
> Luís
>
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