[postgis-users] Convert from 3067 to 2393

[Pena Kupen]

I add +towgs4 to proj4text, conversion is working ok with sql below.

Thank's for your help and clarifying this!

--
AJL

Ralf Suhr [Ralf.Suhr at itc-halle.de] kirjoitti: 
> Hi Pena,
> 
> changing proj4text is almost save. EPSG:31467 as example have more then 3 
> different towgs84. A better transformation can be NTv2 (+nadgrid parameter) 
> with accuracy in centimeters or use towgs84 from 
> http://www.kolumbus.fi/eino.uikkanen/geodocsgb/ficoords.htm with max error 
> 2meters.
> 
> The towgs84 parameter will only be affected in transformation from/ to wgs84 
> ellipsoid. A direct transformation from ellipsoid "intl" to ellipsoid "grs80" 
> will not use towgs84 parameter. That's a transformation will go intl->wgs84-
> >grs80. One poor workaround is defining EPSG:3067 as "+proj=utm +zone=35 
> +ellps=WGS84".
> 
> Gr
> Ralf
> 
> Am Freitag 04 März 2011, 13:13:27 schrieben Sie:
> > Ralf,
> > 
> > On our spatial_ref_sys at 2393 there is proj4text as
> > +proj=tmerc +lat_0=0 +lon_0=27 +k=1.000000 +x_0=3500000 +y_0=0 +ellps=intl
> > +units=m +no_defs
> > 
> > It seems that +towgs4 is missing? If I change this, it it safe?
> > 
> > Do you mean like this?
> > select x(ST_Transform(ST_Transform( tbl.p, 4326),2393)),
> > y(ST_Transform(ST_Transform( tbl.p, 4326),2393)) from (select
> > GeomFromText('POINT(108043 6683685)',3067) as p) as tbl
> > 
> > Result is same as before as:
> > 3107866.533 6686516.654
> > 
> > --
> > Pena
> > 
> > Ralf Suhr [Ralf.Suhr at itc-halle.de] kirjoitti:
> > > Hi Pena,
> > > 
> > > first verify EPSG:2393 is set with correct towgs84 parameters in
> > > spatial_ref_sys (http://spatialreference.org/ref/epsg/2393/proj4/).
> > > 
> > > Because the destination EPSG is not based on WGS84 ellipsoid you have to
> > > transform twice: ST_Transform( ST_Transform( POINT_FROM_3067, 4326),
> > > 2393)
> > > 
> > > Gr
> > > Ralf
> > > 
> > > Am Freitag 04 März 2011, 11:53:44 schrieb Pena Kupen:
> > > > Hello all,
> > > > 
> > > > I try to do some conversion between different coordinates (3067 to 2393
> > > > ) without saving them to database. My sql is following:
> > > > select x(ST_Transform(tbl.p,2393)), y(ST_Transform(tbl.p,2393)) from
> > > > (select GeomFromText('POINT(108043 6683685)',3067) as p) as tbl
> > > > 
> > > > result:
> > > > 3107866.533 6686516.654
> > > > 
> > > > Correct one is:
> > > > 3108053.305 6686493.081
> > > > 
> > > > location is about 200m too much on west.
> > > > 
> > > > Any ideas?
> 
> 


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