R: R: [postgis-users] precision of GeomFromTex, Transform and text functions

Tue Sep 4 07:43:33 PDT 2007

There's no FROMWGS parameter, TOWGS is all that's needed,
as far as I know.
Problem may be that the coordinates you are using have
a longitude (37.xxxx) not inside Italy (actually they apper to be 
somewhere in southern Russia near the Georgia border).
If you do the insert/select using coordinates like:
	9.13953463591601 45.66405322544534

it should work as expected.

Bye
Paolo Rizzi

> -----Messaggio originale-----
> Da: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net]Per conto di
> Ludovico Bianchini
> Inviato: martedì 4 settembre 2007 16.02
> A: PostGIS Users Discussion
> Oggetto: Re: R: [postgis-users] precision of GeomFromTex,Transform and
> text functions
> 
> 
> Thanks for the suggestion, actually there were not the
> toWGS parameter in spatial_ref_sys table.
> 
> The situation seems to be a little better (here a
> sequence of insert-select:
> Insert:37.13953463591601 45.66405322544534
> Select:37.1321637582786 45.6647731135686
> 
> Insert:37.1321637582786 45.6647731135686
> Select:37.1248123607135 45.6654908577754
> 
> Insert:37.1248123607135 45.6654908577754
> Select:37.1174803443424 45.6662064695791), but the
> error is still too big.
> 
> I have this question: is there a parameter simmetric
> to TOWGS? If so the project library shall use FROMWGS
> to convert from the gps system and TOWGS to convert to
> the gps system.
> Sorry if the question is stupid, but I don't
> understand how to solve this problem (to convert gps
> (SRID=4326) to West Gauss Boaga Italy Rome Monte Mario
> (SRID=26591 or 3003).
> 
> Any help will be very appreciated!!!
> 
> Ludovico
> 
> 
> --- P.Rizzi Ag.Mobilità Ambiente
> <paolo.rizzi at ama-mi.it> ha scritto:
> 
> > I forget to mention the fact that inside the PostGIS
> > spatial_ref_sys
> > table, TOWGS parameters are missing for EPSG:26591
> > and for 3003 too.
> > So any transform will not be precise in any case.
> > To add parameters for EPSG:3003, you can use the
> > following SQL
> > in any DB that you need to.
> > 
> > Bye
> > Paolo Rizzi
> > 
> > 
> > ---
> > --- To add TOWGS parameters, if needed, to:
> > ---
> > --- EPSG 3003 : Monte Mario / Italy zone 1
> > ---
> > --- If parameters are already present, no change
> > will take place.
> > ---
> > UPDATE "spatial_ref_sys" SET
> > "srtext"='PROJCS["Monte Mario / Italy zone
> > 1",GEOGCS["Monte
> > Mario",DATUM["Monte_Mario",SPHEROID["International
> >
> 1924",6378388,297,AUTHORITY["EPSG","7022"]],TOWGS84[-104.1,-49
> .1,-9.9,0.971,-2.917,0.714,-11.68],AUTHORITY["EPSG","6265"]],P
> RIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.
> 01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","
> 4265"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_
> of_origin",0],PARAMETER["central_meridian",9],PARAMETER["scale
> _factor",0.9996],PARAMETER["false_easting",1500000],PARAMETER[
> "false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],A
> UTHORITY["EPSG","3003"]]'
> > WHERE "srid"=3003 AND "auth_name"='EPSG' AND
> > "srtext" NOT LIKE '%TOWGS%';
> > 
> > UPDATE "spatial_ref_sys" SET
> > "proj4text"='+proj=tmerc +lat_0=0 +lon_0=9
> > +k=0.999600 +x_0=1500000 +y_0=0 +ellps=intl +units=m
> > +no_defs
> >
> +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68'
> > WHERE "srid"=3003 AND "auth_name"='EPSG' AND
> > "proj4text" NOT LIKE '%towgs%';
> > 
> > 
> > 
> > 
> > > -----Messaggio originale-----
> > > Da: postgis-users-bounces at postgis.refractions.net
> > >
> >
> [mailto:postgis-users-bounces at postgis.refractions.net]Per
> > conto di
> > > P.Rizzi Ag.Mobilità Ambiente
> > > Inviato: martedì 4 settembre 2007 11.25
> > > A: PostGIS Users Discussion
> > > Oggetto: R: [postgis-users] precision of 
> > > GeomFromTex,Transform and text
> > > functions
> > > 
> > > 
> > > Probably it does not matter to you in this case,
> > > but EPSG:26591 has been deprecated in favour of
> > EPSG:3003.
> > > There is an error (can't remember what) in 26591.
> > > 
> > > Bye
> > > Paolo Rizzi
> > > 
> > > 
> > > > -----Messaggio originale-----
> > > > Da:
> > postgis-users-bounces at postgis.refractions.net
> > > >
> >
> [mailto:postgis-users-bounces at postgis.refractions.net]Per
> > conto di
> > > > Ludovico Bianchini
> > > > Inviato: lunedì 3 settembre 2007 21.39
> > > > A: postgis-users at postgis.refractions.net
> > > > Oggetto: [postgis-users] precision of
> > GeomFromTex,Transform and text
> > > > functions
> > > > 
> > > > 
> > > > Hi all,
> > > > 
> > > > I'm using this postgis function:
> > > > - GeomFromText(text, int4) to create a geometry
> > value
> > > > in 4326 spatial_ref_sys
> > > > - Transform(geometry, int4) to convert a
> > geometry from
> > > > 4326 to 26591 when I'm inserting a record and to
> > > > convert 26591 to 4326 when I'm selecting records
> > > > - text(geometry) to convert the geometry column
> > in a
> > > > human-readable string
> > > > 
> > > > The problem is that the operations are not
> > precise:
> > > > the value I obtain via
> > text(transorm(geom_column,
> > > > 4326)) is different from what I inserted via 
> > > > Transform(GeomFromText('POINT(' || $10 || ')',
> > 4326),
> > > > 26591).
> > > > 
> > > > Here an example (lon-lat values separated by a
> > space):
> > > > Insert:37.13953463591601 45.66405322544534
> > > > Select:37.1321614399253 45.6647733181425
> > > > 
> > > > Insert:37.1321614399253 45.6647733181425
> > > > Read:37.1248077366115 45.6654912656918
> > > > 
> > > > Insert:37.1248077366115 45.6654912656918
> > > > Read:37.1174734269995 45.6662070796171
> > > > 
> > > > Is this a 'normal' behaviour?
> > > > Am I omitting anything?
> > > > 
> > > > Thanks in advance for any help!!
> > > > 
> > > > Bye,
> > > > Ludovico 
> > > > 
> > > > 
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