I add +towgs4 to proj4text, conversion is working ok with sql below.
Thank's for your help and clarifying this!
--
AJL
Ralf Suhr [ralf.s...@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.s...@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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