[postgis-users] problems with transformation

[Obe, Regina]

I know for certain projections the answers between 4.5 and 4.6 are different.  I ran into that issue myself.  So I suspect your problem is the difference
in PROJ and not PostGIS.

I think you many need to change the proj4text in 4.6  to make it agree with old by adding an extra parameter.  I forget what that is.  I think the old 4.5 made an assumption of what that paramter is when its not present and 4.6 doesn't.

Thanks,
Regina
 

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Stefan Zweig
Sent: Thursday, September 18, 2008 7:45 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] problems with transformation

hi list,

im a using two different installations of postgis. the first (1.) is for testing the second (2.) for working.


(1.)
select postgis_full_version()
"POSTGIS="1.3.3" GEOS="3.0.0-CAPI-1.4.1" PROJ="Rel. 4.6.0, 21 Dec 2007" USE_STATS"

(2.)
select postgis_full_version()
"POSTGIS="1.2.1" GEOS="2.2.3-CAPI-1.1.1" PROJ="Rel. 4.5.0, 22 Oct 2006" USE_STATS"


i am running the same query on both installations, getting different results:

(1.)
select st_y (transform(setsrid(makepoint(-626172.139189,7514065.62361),9805), 4326));
55.7765729937296

(2.)
select st_y (transform(setsrid(makepoint(-626172.139189,7514065.62361),9805), 4326));
55.9549116318344

the content for the srids 4326 and 9805 is equal on both installations:

(1.) + (2.)
select * from spatial_ref_sys where srid = 4326 or srid = 9805

srid;auth_name;auth_srid;srtext;proj4text
4326;EPSG;4326;GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]];+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
9805;EPSG;9805; ;+proj=merc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +units=m +no_defs


actually i would suppose to get same results on both installations using transform() if the srid entries on both installations are equal. is there another point than the spatial_ref_sys table where the coordinate systems information can be set?

to me it seems like installation (1.) calculates the transformation using a spheroid and (2.) using the wgs84 ellipsoid.


any advices?
thanks in advance + regards. stefan
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