[R-sig-Geo] Change in proj strings?

[Roger Bivand]

On Wed, 20 May 2015, Tim Keitt wrote:

> I get: Error in CRS("+proj=longlat") : major axis or radius = 0 or not given
>
> Never seen that before. What's the fix?

Depending on platform, you see different consequences.

When PROJ.4 parses a string defining a spatial reference system, it wants 
something to give it a metric. The +ellps= tag is one such. In PROJ_LIB, 
there used to be a file (proj_def.dat), which contained +ellps=WGS84 as a 
default. On seeing any incoming string without any tags giving ellipsoid 
details, the default was used.

The PROJ.4 trunk still has proj_def.dat, and up to and including 4.8.0, it 
was always shipped in the source and binaries (like Debian proj-data). 
Because the file seems to have been left out of 4.9.*RC* and 4.9.1, anyone 
deleting PROJ_LIB before installing the new version will lose access to 
the defaults. You can avoid using this file by saying:

CRS("+proj=longlat +no_defs")

and indeed that is why +init= generated parsed strings have +no_defs (no 
defaults) set - they ignore proj_def.dat.

I've entered a PROJ.4 ticket #274 about missing proj_def.dat in released 
4.9.1, and posted on the proj list without response so far.

CRAN installed the Debian 4.9.1 packages on Monday with considerable 
fall-out, and many package maintainers have been contacted (some as early 
as the RC for 4.9.* by me and Edzer).

One way to look at this is as a wake-up call reminding us that a metric 
really is needed in a spatial reference system definition. However, PROJ.4 
has broken its earlier practice of providing a reasonable default, very 
likely by mistake.

The current status for CRAN is that Windows and Snow Leopard rgdal binary 
packages include proj_def.dat, OSX Mavericks does not (but will be rebuilt 
today, thanks to Simon Urbanek, so may get it - hard to inject 
automatically), and installs of rgdal from source depend on the platform 
PROJ.4. The recent Debian release is without proj_def.dat. The file itself 
may be added to PROJ_LIB manually, and downloaded from:

http://trac.osgeo.org/proj/browser/trunk/proj/nad/proj_def.dat

(unchanged in 14 years and very simple). I have no idea how it got lost 
from the PROJ.4 source distribution, but it isn't in proj-4.9.1/nad of:

http://download.osgeo.org/proj/proj-4.9.1.tar.gz

These things are sent to try us ...

Roger

>
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> http://www.keittlab.org/
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no