[GRASS-dev] Plan to build Package to use GRASS from R

[Roger Bivand]

Glynn Clements wrote:
> 
> 
> Rainer M Krug wrote:
> 
>> Sorry for crossposting, but I think this can be of interest for GRASS and
>> R
>> users.
>> 
>> I am planning to write a package to make the use of GRASS from R easier.
>> The
>> idea is to wrap the system call to execute the GRASS command into an R
>> command of the same name.
>> e.g:
>> r.to.vect <- function(..., intern=TRUE, ignore.stderr=FALSE)
>>   {
>>     comm <- paste( "r.to.vect ", ..., sep="" )
>>     print(comm)
>>     system( comm, intern=intern, ignore.stderr=ignore.stderr )
>>   }
>> 
>> My questions are:
>> 
>> 1) Is this a good way of doing it, or is giving a named list to the
>> function
>> more usefull?
> 
> If R provides a way to pass individual arguments (argc/argv), use that
> instead of contructing a shell command as a string. Otherwise, you are
> likely to run into problems with shell metacharacters in argument
> values.
> 
> (Replying in Nabble because Rainer's posting has been swallowed by
> threading everywhere else)
> 
> This is the key sympton, seen recently in a similar interface to SAGA,
> where the package author carelessly converted all "/" to "\" (it is only
> on Windows), thus destroying a valid r.mapcalc-like operation.
> 
> It is made worse by differences between Unixen and Windows in handling
> stdout and stderr, and by differences between CygWin and MSYS in what the
> GRASS commands are called in system() - MSYS wants an *.exe.
> 
>> 2) Is there a way to obtain easily all commands from GRASS and the
>> parameters possible and required?
> 
> You can obtain a list of commands by enumerating the $GISBASE/bin and
> $GISBASE/scripts directories. Nearly all commands support the
> --interface-description switch, which outputs details of all of the
> options in XML. There are several other switches which output the same
> information in different formats; see the g.parser manpage for
> details.
> ---
> Actually, the interface problem for R is almost exactly the same as for
> all the other front ends - think of R as a CLI-UI. Using XML in R to set
> up commands going from R to GRASS might not be impossible, where there
> would be only one command - do_GRASS(), taking the GRASS command as its
> required argument, and relying on the GRASS GUI to put up a dialogue. If
> there were further arguments, then they would be used in the context of
> the requested command. 
> 
> I haven't been following the GUI discussion, so wonder whether the
> --interface-description output is cached anywhere? If not, do_GRASS()
> would retrieve that first, and then try to insert given arguments, using
> platform specific "glue" to move forward. Has the (excellent, by the way)
> progress on GUI provided a way of passing a "bubble" (say in XML) to GRASS
> commands, to avoid having to step around shell metacharacters? The same
> for error handling? It feels as though g.parser will help a lot.
> 
> Roger
> -- 
> Glynn Clements <glynn at gclements.plus.com>
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> 
> 

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