[postgis-users] Using grids transformation method with PostGis

[Luís de Sousa]

Hello everyone,

I finally found out what was wrong, in PostGis 1.4 the EPSG 3763 srid
is ill defined or incomplete. Basically it is missing the
'towgs84=0,0,0' parameter, though in my understanding it isn't used
during a grids transformation. Please see the attached log.

This is bewildering. I found this by mere chance, when on another list
someone wrote that EPSG 3763 was only made available in PostGis 1.5.
Not exactly that, in prior versions it simply seems to be incomplete.

Best regards and thanks to all for your time,

Luís
-------------- next part --------------
pontosDTU=> select ST_AsText(ST_Transform(ST_SetSRID(ST_Makepoint(-74584.120,2459.620), 20791), 3763));
                 st_astext                 
-------------------------------------------
 POINT(-74477.6196590331 2281.82581261639)
(1 row)

pontosDTU=> DELETE FROM spatial_ref_sys WHERE srid = 3763;
DELETE 1
pontosDTU=> INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext)
pontosDTU-> values ( 3763, 'epsg', 3763,
pontosDTU(> '+proj=tmerc +lat_0=39.66825833333333 +lon_0=-8.133108333333334 +k=1 +x_0=0 +y_0=0 +ellps=GRS80 +units=m +towgs84=0,0,0',
pontosDTU(> 'PROJCS["ETRS89 / Portugal TM06",GEOGCS["ETRS89",DATUM["European_Terrestrial_Reference_System_1989",SPHEROID["GRS 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6258"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4258"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",39.66825833333333],PARAMETER["central_meridian",-8.133108333333334],PARAMETER["scale_factor",1],PARAMETER["false_easting",0],PARAMETER["false_northing",0],AUTHORITY["EPSG","3763"],AXIS["X",EAST],AXIS["Y",NORTH]]');
INSERT 0 1
pontosDTU=> select ST_AsText(ST_Transform(ST_SetSRID(ST_Makepoint(-74584.120,2459.620), 20791), 3763));
                 st_astext                 
-------------------------------------------
 POINT(-74582.5663449779 2460.86030110706)
(1 row)