I am trying to change the SRID of polygons layer, but I'm having trouble visualizing the result.
I the SRID is misreported the shapefile I used to import into PostGIS. The metadata says the reference system is SIRGAS2000. However looking how the data is "drifted" (see image) I suspect the true SRID could be 4618 (SAD69)
So I tried updating the SRID (without changing the underlying points, etc) in Postgis:
Update_GeometrySRID('setor_censitario_2','geom',4618)and compared the results of the SRID update polygons to to the original polygons in Qgis.
Nothing changed, both layers seem identical.
This puzzled me. Shouldn't they have changed? The parameters of the two "data" (SIRGAS2000 and SAD69) are indeed different in a non-negligible way. So, just to make sure the change of SRID was not supposed to be innocuous, I ST_Tranformed the geom:
create table setor_censitario_4 as select geom, ST_Transform(geom,4291) as geom4291Transf, ST_Transform(geom,4618) as geom4618Tranf from setor_censitarionow the new geom is different from the original one. ST_Transform, of course, is not the correction I want (in fact I doubled the magnitude of the problem).
So why is Update_GeometrySRID not changing the location of the polygons in Qgis?
The shapefile is available from: ftp://geoftp.ibge.gov.br/malhas_digitais/censo_2010/setores_censitarios/ba.zipafter unziping I imported with:
shp2pgsql -c -s -I -W LATIN1 file public schema.table ...
أكثر...
I the SRID is misreported the shapefile I used to import into PostGIS. The metadata says the reference system is SIRGAS2000. However looking how the data is "drifted" (see image) I suspect the true SRID could be 4618 (SAD69)
So I tried updating the SRID (without changing the underlying points, etc) in Postgis:
Update_GeometrySRID('setor_censitario_2','geom',4618)and compared the results of the SRID update polygons to to the original polygons in Qgis.
Nothing changed, both layers seem identical.
This puzzled me. Shouldn't they have changed? The parameters of the two "data" (SIRGAS2000 and SAD69) are indeed different in a non-negligible way. So, just to make sure the change of SRID was not supposed to be innocuous, I ST_Tranformed the geom:
create table setor_censitario_4 as select geom, ST_Transform(geom,4291) as geom4291Transf, ST_Transform(geom,4618) as geom4618Tranf from setor_censitarionow the new geom is different from the original one. ST_Transform, of course, is not the correction I want (in fact I doubled the magnitude of the problem).
So why is Update_GeometrySRID not changing the location of the polygons in Qgis?
The shapefile is available from: ftp://geoftp.ibge.gov.br/malhas_digitais/censo_2010/setores_censitarios/ba.zipafter unziping I imported with:
shp2pgsql -c -s -I -W LATIN1 file public schema.table ...
أكثر...