[Bug 368065] [NEW] Cartographic projection library (proj) built without datum conversion grid data

[tvrusso]

Public bug reported:

Binary package hint: proj

I am using Ubuntu 8.04 (Hardy).  This bug report pertains to the
proj-4.6.0_1 package, which I no longer have installed due to this bug
(I've installed from source instead).

The cartographic projection library, proj, is advertised as now
containing built-in datum conversion capability.  Yet in all the binary
packages I have checked (in Hardy and in Intrepid), the binary has been
built without the NAD27/NAD83 datum conversion grid data.

Without this data, attempts to use libproj to convert between NAD27 and
NAD83 result in no datum conversion at all (this is a flaw in the
design, IMHO, because it should *TELL* you that there's a problem
instead of just doing nothing, but that's not Ubuntu's fault).  To
demonstrate the issue, enter the following command on a system that has
had the proj-4.6.0 binary installed:

cs2cs +proj=latlong +datum=NAD27 +to +proj=latlong +datum=NAD83

This command should take longitude/latitude coordinates in NAD27 datum and transform them to NAD83 datum.    Give it the following input:
106d35'27"W 36d10'15"N

The correct output would be:
106d35'29.13"W  36d10'15.063"N 0.000

which represents the correct datum shift between NAD27 and NAD83.
Conversion between these two datums is impossible without the grid shift
data due to the nature of the shift (which is non-uniform across the
continent and must be tabulated).

On all versions of Ubuntu on which I've tried this, the answer is
incorrect, returning instead exactly the same coordinates as the input.
The error can be large --- in my part of the country, the error is 50
meters of east/west shift not being properly applied.

This indicates that the datum conversion grids were not added to the
source code when the package was built.  To build proj with the datum
grids one has to do this (I am using the proj-4.6.1 source code to
demonstrate, but it applies to 4.6.0 as well):

wget ftp://ftp.remotesensing.org/proj/proj-4.6.1.tar.gz
wget ftp://ftp.remotesensing.org/proj/proj-datumgrid-1.4.tar.gz

tar xzf proj-4.6.1.tar.gz
cd proj-4.6.1/nad
tar xzf ../../proj-datumgrid-1.4.tar.gz
cd ..
./configure --prefix=/usr && make

The build will now properly convert datums between NAD83 and NAD27.
Without the proj-datumgrid-1.4.tar.gz file being first untarred in the
"nad" directory before building, the result is incorrect.  This is a
serious error when proj libraries are used in GIS software on data for
North America, and the packages should be rebuilt for all versions of
Ubuntu.  I am told that this problem also exists in several other
Debian-based systems such as Mepis.

Until the package is corrected, users of proj in North America would be
advised to install from source using the instructions above rather than
using the package.  The package "libgeotiff" requires the "proj"
package, so users of libgeotiff will have to install that package from
source as well.

** Affects: proj (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Cartographic projection library (proj) built without datum conversion grid data
https://bugs.launchpad.net/bugs/368065
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