help pages for CRS duplicated?

On Wed, 25 Mar 2009, Don MacQueen wrote:

I encountered the following. My quick and simple search of past 
emails in R-sig-geo didn't find any previous discussion.

 search()

".GlobalEnv"        "package:rmacq"     "package:rgdal"
 "package:maptools"  "package:sp"
 "package:foreign"   "package:stats"     "package:graphics"
"package:grDevices" "package:utils"     "package:datasets"
 "package:methods"   "Autoloads"         "package:base"

 find('CRS')

[1] "package:sp"

 ?CRS

Help on topic 'CRS' was found in the following packages:

 Package               Library
 rgdal                 /Library/Frameworks/R.framework/Resources/library
 sp                    /Library/Frameworks/R.framework/Resources/library



Followed by a request to identify which one to view.

Since the behaviour of the class differs depending on whether rgdal 
is available or not, it is described (somewhat differently) in both. 
As it is, sp does not depend on rgdal but rgdal depends on sp, and 
this is likely to continue to be the case. Note that the specific 
versions can be accessed by:

help(CRS, package=sp)
help(CRS, package=rgdal)

Further, the sp version uses examples depending on rgdal through 
require(), but sp does not "Suggest:" rgdal to avoid circularity.

The difference, as the help pages explain, is that in just sp, there 
is no external check of the correctness of the string inserted into 
class instances, while when rgdal is loaded, the strings are checked 
using the PROJ.4 library.

Hope this helps,

Roger

Thanks
-Don


(In case anyone wonders, rmacq is a local personal package.)

 sessionInfo()

R version 2.8.1 (2008-12-22)
i386-apple-darwin8.11.1

locale:
C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] rmacq_1.0-2     rgdal_0.5-30    maptools_0.7-16 sp_0.9-28 foreign_0.8-30

loaded via a namespace (and not attached):
[1] grid_2.8.1      lattice_0.17-17 tcltk_2.8.1     tools_2.8.1
Warning message:
'DESCRIPTION' file has 'Encoding' field and re-encoding is not possible

--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no