[postgis-users] Using grids transformation method with PostGis

[Luís de Sousa]

Dear all,

I'm having the same results with the GISVM. It can provide an easy way
to reproduce this behaviour, here's how:

1. Download the latest GISVM from:
http://sourceforge.net/projects/gisvm/files/GISVM_Release_2/GISVM_Base_Release_2/gisvm2base_20100601.7z/download

2. Run it either with Virtual Box or VMPlayer.

3. Use install scripts to get Proj4 and grid files:
http://gisvm.svn.sourceforge.net/viewvc/gisvm/trunk/gisvm2base/install_proj470.sh
http://gisvm.svn.sourceforge.net/viewvc/gisvm/trunk/gisvm2base/install_grelhas.sh

4. Try it with something like:

user at gisvm:/etc/profile.d$ cs2cs +init=pt:dlxhg +to +init=pt:pttm06
-74584.120 2459.620
-74582.57	2460.86 0.00

user at gisvm:/etc/profile.d$ /etc/postgresql/8.4/bin/psql -h localhost
-d template_postgis -p 5432 -U postgres
Password for user postgres:
psql (8.4.1)
Type "help" for help.

template_postgis=# UPDATE spatial_ref_sys
template_postgis-# SET proj4text = '+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=ptLX_e89.gsb'
template_postgis-# WHERE srid = 20791;
UPDATE 1
template_postgis=# SELECT
X(ST_Transform(PointFromText('POINT(-74584.120 2459.620)', 20791),
3763)),
template_postgis-# Y(ST_Transform(PointFromText('POINT(-74584.120
2459.620)', 20791), 3763));
         x         |        y
-------------------+------------------
 -74477.6196590331 | 2281.82581261726
(1 row)

Hope it can shed some light on what may be happening. Thank you,

Luís