Re-2: [Proj] GK31_Tirol (Austria)

[Jens Schwarz]

Hello Frank,

thanks again!

-------- Original Message --------
Subject: Re: [Proj] GK31_Tirol (Austria) (20-Apr-2007 15:02)
From:    Frank Warmerdam <warmerdam at pobox.com>
To:      jens.schwarz at alpstein.de

> Jens Schwarz wrote:
> > 
> > Hello Frank,
> > 
> > thanks for your help!
> > cs2cs works now. I didn't see that the parameter is called towgs84 for proj 
> > and towgs for cs2cs.
> 
> Jens,
> 
> It is towgs84 everywhere.  Is there some documentation in conflict with 
> this?
> If so, let me know and I'll fix it.

proj ignores towgs84 (as far as I can reproduce it):

proj +proj=tmerc +ellps=bessel +lat_0=0 +lon_0=13.333333 +k=1.000000 +x_0=0 +y_0=-5000000 +towgs84=577.326,90.129,463.919,5.1366,1.4742,5.2970,2.4232 -r<<EOF
> 47.487218 12.254853
> EOF
-81265.97       261441.61

proj +proj=tmerc +ellps=bessel +lat_0=0 +lon_0=13.333333 +k=1.000000 +x_0=0 +y_0=-5000000 -r<<EOF
> 47.487218 12.254853
> EOF
-81265.97       261441.61

But:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +ellps=bessel +lat_0=0 +lon_0=13.333333 +k=1.000000 +x_0=0 +y_0=-5000000 +towgs84=577.326,90.129,463.919,5.1366,1.4742,5.2970,2.4232 -r<<EOF
> 47.487218 12.254853
> EOF
-81220.59       261502.07 -47.76

I couldn't get the right result with proj, only with cs2cs (and your help).
I wondered if/how postgis decides when to use proj or cs2cs.

> 
> > I need it in postgis. I don't know if it would be enough to set the cs2cs 
> > parameter string as proj4text there.
> > I'll ask their mailing list.
> 
> You should be able to use the same coordinate system in proj4text
> as you used on the cs2cs commandline.

I tried to do it brute force and did the following in postgis:

select * from spatial_ref_sys where srid=31255;

 srid  | auth_name | auth_srid | srtext |           proj4text                               
-------+-----------+-----------+--------+---------------------------------------------------------------
 31255 |           |           |        | +proj=tmerc +ellps=bessel
                                          +lat_0=0 +lon_0=13.333333 +k=1.000000
                                          +x_0=0 +y_0=-5000000
                                          +towgs84=577.326,90.129,463.919,5.1366,1.4742,5.2970,2.4232


select AsText(Transform(PointFromText('POINT(47.487218 12.254853)',4326),31255));

                  astext
-------------------------------------------
 POINT(3933583.45695887 -3371941.86007218)

I'm confused as it's not right and not the same as proj on command line.

> 
> > As we're running web applications, we're also using the javascript port of 
> > proj.
> > The cs2cs port isn't there yet.
> 
> Ah, well the javascript library is a completely different implementation so
> you do have to be wary about compatability issues.
> 
> Best regards,
> -- 

Best regards.