[postgis-users] NAD conversion problem

[Dylan Beaudette]

On Tuesday 09 December 2008, Peter N. Schweitzer wrote:
> Richard Greenwood wrote:
> > On Mon, Dec 8, 2008 at 12:19 PM, Peter N. Schweitzer
> >
> > <pschweitzer at usgs.gov> wrote:
> >> Richard Greenwood wrote:
> >>> On Thu, Dec 4, 2008 at 1:19 PM, Peter N. Schweitzer
> >>>
> >>> <pschweitzer at usgs.gov> wrote:
> >>>> Hello,
> >>>>
> >>>> I have two PostgreSQL installations.  One uses 8.3.3 with PostGIS
> >>>> 1.3.3, GEOS 3.0.1, and PROJ 4.6.1 (with proj-datumgrid-1.4).  With it
> >>>> I am able to
> >>>> run a command like
> >>>>
> >>>> update county set nad27_geom=ST_Transform(the_geom,4267);
> >>>>
> >>>> My newer installation uses 8.3.5 with PostGIS 1.3.4, GEOS 3.0.3, and
> >>>> PROJ 4.6.1.  With this system I get the error message
> >>>>
> >>>> WARNING:  transform: -38 (failed to load NAD27-83 correction file)
> >>>> ERROR:  transform: couldn't project point: -38 (failed to load
> >>>> NAD27-83 correction file)
> >>>>
> >>>> I know that proj-datumgrid-1.4.zip must be unzipped in the nad/
> >>>> directory of proj-4.6.1 PRIOR to running configure.  I have done this.
> >>>> I have also recompiled and reinstalled proj, GEOS, and PostGIS in that
> >>>> order, running ldconfig at the end of each step.  The directory
> >>>> /usr/local/share/proj on each of these systems is identical.
> >>>>
> >>>> I've tried recreating the database cluster, starting and stopping
> >>>> the database instance, rebooting the machine, dropping and rebuilding
> >>>> the spatial database, all to no avail.
> >>>>
> >>>> So I'm looking for some setting that I may have missed, some
> >>>> environment variable, or some trick to tell libproj.so.0.5.5 where its
> >>>> transform files should go.
> >>>>
> >>>> Both systems run Slackware 12.1.
> >>>>
> >>>> I'm at wit's end.  Any clues?
> >>>>
> >>>> Pete
> >>>
> >>> PROJ_LIB is an environment variable that points to the directory
> >>> containing grid shift files and EPSG parameter files.
> >>>
> >>> The grid shift files are binary and platform specific. Is it possible
> >>> that you are using Windows grid shift files on a Linux system?
> >>>
> >>> You could also rule out issues related to the different versions of
> >>> Postgres and PostGIS on you two systems by testing at the command line
> >>> with the cs2cs utility which is a part of Proj.
> >>
> >> Rich,
> >>
> >> Thanks for your counsel.  The example using cs2cs from its documentation
> >> worked the same on both systems, executed from the command line.
> >>
> >> I believe the grid shift files are slightly different, even though I
> >> thought I had installed the same versions.  As a test, I copied the
> >> /usr/local/share/proj directory from the older system (the one that
> >> does the datum shift without complaint) to the newer one, and the
> >> ST_Transform completes without error.  So I believe that is the source
> >> of the problem.
> >>
> >> But there is only one link on http://trac.osgeo.org/proj/ for the datum
> >> shift file package.  If the package is OS-specific I would
> >> expect to see more than one.  So I am puzzled and worried that next
> >> time I may face the same problem again.
> >>
> >> Peter
> >
> > The files in http://svn.osgeo.org/metacrs/proj/trunk/proj/nad/ are
> > ASCII. In the nad directory, you need to do:
> >   ./configure
> >   make
> >   install
> > to create the binary grid shift files that proj actually uses. (Proj
> > doesn't read the ASCII files). And I'm not sure that the
> > config-make-install of the proj program does the nad directory.
> >
> > Rich
>
> Many thanks to Rich and Dylan for helpful replies.
>
> I was able to trace the problem to a file in the proj source code.
>
> in proj-4.6.1/src/pj_datums.c
> 87,88c87,88
> < "NAD27",    "nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat",
> <                                                      "clrk66",
> ---
>
> > "NAD27",    "nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat, at null",
> >                                                      "clrk66",
>
> I don't recall when I added the ", at null" to the nadgrids= line, but I
> think it was in response to someone else's urging.  And adding it to
> the current source causes proj to correctly locate the conversion
> files.  I don't know whether this is a bug in proj or a peculiarity
> of the systems where I've deployed it.
>
> Thanks again for your help!
>
> Peter

Strange. I have never modified that code before, and regularly get the correct 
output... I will post back with a similar example that causes PostGIS to 
throw the '-38' error.

Cheers,

Dylan


-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341