On Thu, Sep 29, 2011 at 8:50 PM, Jonathan Greenberg <jgrn@illinois.edu>wrote:

> Thanks for the responses -- one of the issues with the GRASS
> implementation of terraflow is that there is not, to my knowledge,
> parallel support for the code -- the C++ version, I suppose, we can
> try to compile, although it seems to be fairly out of date.  I figured
> with the quickly increasing capabilities in spatial programming beyond
> just spatial statistics in R (e.g. via raster, rgdal, maptools), as
> well as other people developing parallel interfaces for R (e.g.
> snowfall, Rmpi), R may do well as a scalable system for doing large
> scale image processing/GIS analyses.  Certainly, other programs have
> not scaled well (ArcMap and GRASS to name a few).
>

If you would like to process large maps, I would definitely go the GRASS
route, and adopt the C code, so that it utilises multiple cores. i would
actually suggest to get in contacts with the developers as they might give
you some input and ideas. I would definitely not go the route of doing the
computations directly in R, as that would sloe does the analysis. If you
have the parallel implementation in GRASS, you could use it from R. Another
option would be to adapt the C implementation used in GRASS to be called
directly from R, and that you simply provide the names of the rasters and
the C routines are doing the rest and returning the names of the resulting
maps.

I thought quite a few times, that one implementation in a C library of these
kinds of algorithms, so that they could be used from GRASS and R, with
simple wrappers - A framework like that would be very useful for GRASS and
R.

Cheers and keep us posted,

Rainer


>
> topidx looked interesting but I can tell that it won't scale -- it
> requires the image be in memory as a matrix, so any reasonably large
> DEM won't work.
>
> Sounds like this may require some programming!
>
> --j
>
>
>
> On Thu, Sep 29, 2011 at 6:02 AM, Rich Shepard <rshepard@appl-ecosys.com>
> wrote:
> > On Wed, 28 Sep 2011, Jonathan Greenberg wrote:
> >
> >> I was wondering if anyone had implemented flow accumulation in R (e.g.
> >> http://www.cs.duke.edu/geo*/terraflow/)?
> >
> > Jon,
> >
> >  I use r.terraflow (and other hydrological modules) within GRASS
> > <http://grass.osgeo.org/>. Terrain and hydrologic modeling is best done,
> in
> > my opinion, in GRASS and leave the spatial statistics to R. There is an
> > interface between the two that allows us users to take advantage of both.
> >
> > Rich
> >
> > --
> > Richard B. Shepard, Ph.D.          |   Integrity - Credibility -
> Innovation
> > Applied Ecosystem Services, Inc.   |    Helping Ensure Our Clients'
> Futures
> > <http://www.appl-ecosys.com>     Voice: 503-667-4517      Fax:
> 503-667-8863
> >
>
>
>
> --
> Jonathan A. Greenberg, PhD
> Assistant Professor
> Department of Geography
> University of Illinois at Urbana-Champaign
> 607 South Mathews Avenue, MC 150
> Urbana, IL 61801
> Phone: 415-763-5476
> AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307, Skype: jgrn3007
> http://www.geog.illinois.edu/people/JonathanGreenberg.html
>
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-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology,
UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

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