[STATSGRASS] using R and gstat inside a C module

[Roger Bivand]

On Mon, 23 Oct 2006, G. Allegri wrote:

> I need to use R and gstat functionalities inside a module I'm writing.

Why? What OS/platform? Unless you are doing something very peculiar, you 
will waste an inordinate amount of time, where a shell script will get you 
there simply and be several orders of magnitude easier to debug. Be aware 
that R functions are often best used interactively because user choices 
and error conditions do matter.

> To embed R in a C program libRmath should be used.

No, that is just to use the math functions. See Section 8.1 in 

http://cran.r-project.org/doc/manuals/R-exts.html

for Unixalikes (building R as a shared library, most likely libR.so).

> First question:
> Is it possible to load gstat package from the R standalone library?

Yes, like any package, but why?

> Second question:
> Is there another way to do it when working inside a GRASS module? The
> question raises because, with regard to spgrass6, there's no way to
> use it from a module (except by making a shell process call from C)...

Well, you can use the GRASS API to populate the appropriate R object 
structures in C (see the GRASS5 GRASS package C code).

> am I wrong?

Yes, because you will never (at least for a definition of never being 
greater than the number of developer hours taken to write and maintain 
gstat and the R/GRASS interface) be able to do this robustly, taking 
account of all possible error conditions (identical points passed to gstat 
for example), and track changes in the different software environments 
(something that works only with GRASS version x.y.z, R version a.b.c, 
gstat version d.e.f, sp version g.h.i, etc. There is simply too much being 
patched for a welded-hood C solution to be worth the development and 
maintenance cost.

By the way, you didn't say what you want to do that needs this level of 
automation; if you had, it might be easier to understand your very strange 
design choices and resource commitments.

> Thanks,
> Giovanni
> 
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> statsgrass at grass.itc.it
> http://grass.itc.it/mailman/listinfo/statsgrass
> 

-- 
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