Slope and Aspect calculations in R

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

        

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Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
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