[R-sig-Geo] help pages for CRS duplicated?

[Roger Bivand]

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