[R-sig-Geo] Slope and Aspect calculations in R

[Tomislav Hengl]

Dear Josh, Thomas,

I typically use R+SAGA (R on top!) for such type of analysis (and I do have access to all operating
system/software). There must be some good reasons that I am using SAGA (speed, stability, rich
geomorphometry module etc.)! So do not give up so easy on SAGA.

I especially like that SAGA is fairly efficient in processing big grids, and the commands are rather
compact. For example to reproject grids from one to another proj4string, you only need to set e.g.:

> rsaga.geoprocessor(lib="pj_proj4", 2, param=list(SOURCE_PROJ=paste('"', proj4string(dem25m), '"',
sep=""), TARGET_PROJ="\"+proj=longlat +datum=WGS84\"", SOURCE="TWI.sgrd", TARGET="TWI_ll.sgrd",
TARGET_TYPE=0, INTERPOLATION=0))

*see http://www.geomorphometry.org/R.asp 

I remember that somebody did manage to set-up SAGA also under Mac OS
(http://www.saga-gis.uni-goettingen.de/html/index.php?module=pnForum&func=viewtopic&topic=458), but
I also remember that most of students on our GEOSTAT course used Windows under Mac OS to run SAGA. I
am sure that it should be possible to compile SAGA under Mac OS, but somebody needs to put some
effort to bridge this gap (check also with Olaf Conrad).

Here is more discussion about the same topic from few months ago:
https://stat.ethz.ch/pipermail/r-sig-geo/2009-April/005418.html 

cheers,

Tom Hengl


> -----Original Message-----
> From: r-sig-geo-bounces at stat.math.ethz.ch [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf
> Of Thomas Adams
> Sent: Friday, July 10, 2009 3:12 PM
> To: Josh London
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: [R-sig-Geo] Slope and Aspect calculations in R
> 
> Josh,
> 
> I use R & GRASS together on both MacOS X and Linux without problems.
> It's very direct to write a shell script that calls both R & GRASS
> within a single script. Writing a R script that calls GRASS may be more
> tedious to do what you want. Writing a shell script that calls both may
> be the wat to go.
> 
> Tom
> 
> Josh London wrote:
> > Thanks for the suggestions so far regarding the use of GRASS or SAGA.
> >
> > We have considered those options but SAGA doesn't appear available for
> > MacOS. My understanding is that spgrass6 is more for accessing R
> > code/functions from within GRASS vs accessing GRASS functions from
> > within R. We have all our other analysis coded up in R, and just need
> > these functions to do one part of a bigger process. Maybe I'm
> > misunderstanding how to use R and GRASS together. I'll do some further
> > research.
> >
> > Thanks again
> > Josh
> >
> > Josh London wrote:
> >> Hello
> >>
> >> We are looking to mimic, in R, the slope (max magnitude difference
> >> between a cell and its neighbors) and aspect (direction of maximum
> >> magnitude difference) functions found in ESRI's Spatial Analyst
> >> package. We were just about to code up the slope function but thought
> >> I would make sure we weren't re-inventing any wheels already out there.
> >>
> >> Thanks
> >> Josh
> >>
> >
> 
> 
> --
> Thomas E Adams
> National Weather Service
> Ohio River Forecast Center
> 1901 South State Route 134
> Wilmington, OH 45177
> 
> EMAIL:	thomas.adams at noaa.gov
> 
> VOICE:	937-383-0528
> FAX:	937-383-0033
> 
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