[postgis-users] ST_Transform Incorrect Results?

Wed Oct 20 12:28:06 PDT 2010

Sure thing!

SRID 2163
Server 1: "+proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997
+b=6370997 +units=m +no_defs "
Server 2: "+proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997
+b=6370997 +units=m +no_defs "

SRID 4326
Server 1: "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "
Server 2: "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs "

Unless I am missing something, they both seem to be exactly the same...

I found that earlier as well (forgot to include that as well).  But that
really makes me think it is something with the version of proj4 (or some
data file it might be using?), but maybe someone has other ideas?

On Wed, Oct 20, 2010 at 2:24 PM, Paul Ramsey <pramsey at opengeo.org> wrote:

> Could you show the proj4text strings for your coordinate systems? The
> srtext strings are actually just there for decoration.
>
> P
>
> On Wed, Oct 20, 2010 at 12:16 PM, Josh Abts <josh.abts at vistracks.com>
> wrote:
> > As a followup, the following query reproduces the problem exactly:
> >
> > select astext(st_transform(st_setsrid(st_makepoint(977119.259431679,
> > -252548.899746532), 2163) ,4326))
> >
> > On Server 1 the result is: POINT(-88.11068 42.2810949683921)
> >
> > On Server 2 the result is: POINT(-88.11068 42.0896736466198)
> >
> > It was also mentioned on #postgis to include the differing srtext entries
> I
> > had found on the two servers....
> >
> > For SRID 4326:
> >
> > Server 1 - "GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
> >
> 84",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"]]"
> >
> > Server 2  - "GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
> >
> 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]"
> >
> > For SRID 2163:
> >
> > Server 1 - "PROJCS["US National Atlas Equal Area",GEOGCS["Unspecified
> datum
> > based upon the Clarke 1866 Authalic
> >
> Sphere",DATUM["Not_specified_based_on_Clarke_1866_Authalic_Sphere",SPHEROID["Clarke
> > 1866 Authalic
> >
> Sphere",6370997,0,AUTHORITY["EPSG","7052"]],AUTHORITY["EPSG","6052"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4052"]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_center",45],PARAMETER["longitude_of_center",-100],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","2163"]]"
> >
> > Server 2  - "PROJCS["unnamed",GEOGCS["unnamed
> >
> ellipse",DATUM["unknown",SPHEROID["unnamed",6370997,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_center",45],PARAMETER["longitude_of_center",-100],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1],AUTHORITY["EPSG","2163"]]"
> >
> >
> > On Wed, Oct 20, 2010 at 11:14 AM, Josh Abts <josh.abts at vistracks.com>
> wrote:
> >>
> >> Hello,
> >>
> >> I have been having a problem where I am getting mixed results from two
> >> servers using the same dataset.  The command I am running is as follows:
> >>
> >> select astext(st_transform(start_point,
> >> 4326)),astext(st_transform(end_point, 4326)) from mytable where gid=123
> >>
> >> The two columns are originally using SRID 2163 so I am transforming them
> >> into 4326.  But the results on one server (correct) are different than
> the
> >> results on a second server (incorrect).  They are off by .2 latitude
> >> roughly.
> >>
> >> For example one result set is as follows:
> >>
> >> Server 1 (correct): "POINT(-88.11068 42.2810949683921)";"POINT(-88.10731
> >> 42.2844149305216)"
> >> Server 2 (incorrect): "POINT(-88.11068
> 42.0896736466198)";"POINT(-88.10731
> >> 42.0929914612221)"
> >>
> >> As you can see the longitudes are correctly transformed, but the
> latitude
> >> is not.
> >>
> >> I have also included the postgis_full_version output in case a version
> >> issue might be the culprit.
> >>
> >> Server 1: "POSTGIS="1.3.2" GEOS="3.0.0rc4-CAPI-1.3.3" PROJ="Rel. 4.5.0,
> 22
> >> Oct 2006" USE_STATS"
> >> Server 2: "POSTGIS="1.5.2" GEOS="3.2.2-CAPI-1.6.2" PROJ="Rel. 4.7.1, 23
> >> September 2009" LIBXML="2.7.5" USE_STATS (procs from 1.5 r5385 need
> >> upgrade)"
> >>
> >> So you can see I am using a newer version of PostGIS as well as Proj4
> but
> >> I can't seem to figure out why this would result in an incorrect
> >> St_Transform result.
> >>
> >> I also checked further into the spatial_ref_sys table on both servers
> and
> >> Server 1 has slightly more detailed srtext but they have the same
> proj4text
> >> lines.  I tried copying the srtext from Server 1 to Server 2 and there
> was
> >> no change.
> >>
> >> The only other difference would be the system platforms themselves which
> >> are below.
> >>
> >> Server 1: "PostgreSQL 8.3.4, compiled by Visual C++ build 1400" (this is
> a
> >> windows 2003 server)
> >> Server 2: "PostgreSQL 8.4.5 on x86_64-pc-linux-gnu, compiled by GCC
> >> gcc-4.4.real (Ubuntu 4.4.1-4ubuntu9) 4.4.1, 64-bit"
> >>
> >> Anyone have any ideas of what I could look into to see why I might be
> >> getting this slight variation in results?  I can't find anything that
> would
> >> seem to be the problem or cause of a varying transformation...
> >>
> >> Thanks!
> >> Josh
> >
> >
> >
> > --
> > Joshua Abts
> > IT Specialist
> > VisTracks, Inc.
> > josh.abts at vistracks.com
> > (630) 596-5426
> >
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
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-- 
Joshua Abts
IT Specialist
VisTracks, Inc.
josh.abts at vistracks.com
(630) 596-5426
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