[postgis-users] Using grids transformation method with PostGis

[Fred Lehodey]

Hi,
just a note: we have no problem using the same grids in OS Windows. (tested
with Postgres 8.4 and Postgis 1.4 or 1.5)

HTH,
Fred.


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

> Dear Frank,
>
> Thank you for your message, please read my comments below:
>
> >A few suggestions:
> >
> > * The +nadgrids= directive can include a full path if you want to be
> >   certain that path issues are not coming into play.
>
> I tried this first, the result is exactly the same.
>
> > * If you can ensure that the PROJ_DEBUG environment variable is set to
> >   some value before running the postgres server, you may well see proj
> >   debug output in the terminal window or log for the server.  This should
> >   include information on what grid shift files are picked up and used for
> >   transformations.
>
> Ok, I'll try that next.
>
> > * Your email did not make it clear what the definitions were for
> >   pt:dlxhg, +init=pt:pttm06 or what the proj4text for 3763 is in the
> >   database making it hard to see if the transform was the same as you
> >   did with cs2cs.
>
> Here are the definitions in the /usr/share/proj directory:
>
> # PTTM06 do datum ETRS89
> <pttm06>
> +proj=tmerc
> +ellps=GRS80
> +towgs84=0,0,0
> +lat_0=39d40'05.73"N
> +lon_0=08d07'59.19"W
> <>
>
> # Hayford-Gauss datum Lisboa
> <dlxhg>
> +proj=tmerc
> +ellps=intl
> +nadgrids=ptLX_e89.gsb
> +lat_0=39d40
> +lon_0=8d07'54.862"W
> <>
>
> And here are the strings in the PostGis database:
>
> pontosDTU=# select proj4text from spatial_ref_sys where srid = 20791;
>  +proj=tmerc +lat_0=39.66666666666666 +lon_0=1 +k=1 +x_0=0 +y_0=0
> +ellps=intl +pm=lisbon +units=m +no_defs
> +nadgrids=/usr/share/proj/ptLX_e89.gsb
>
> pontosDTU=# select proj4text from spatial_ref_sys where srid = 3763;
>  +proj=tmerc +lat_0=39.66825833333333 +lon_0=-8.133108333333334 +k=1
> +x_0=0 +y_0=0 +ellps=GRS80 +units=m +no_defs
>
> If you or somebody else want to try it up, the gird files package is
> available from the University of Oporto, courtesy of prof J.A.
> Gonçalves:
>
> http://www.fc.up.pt/pessoas/jagoncal/coordenadas/grelhas.zip
>
> I unpacked all its contents to /usr/share/proj. Btw, my system is Ubuntu
> 9.10.
>
> Before I go, I just want to make sure that in principle PostGis should
> be able to use the grid files simply by the indication of its
> location, no additional configurations needed. Is this correct?
>
> Thank you once more,
>
> Luís
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