[R-sig-Geo] RSAGA .asc morphology loop question

[Alexander Brenning]

Hi Tim,

the rsaga.esri.wrapper currently expects the in.* and out.* arguments 
(with the ASCII/float ESRI grids) to have NO file extension - the file 
extension to be used for all ESRI grids can be given by the 
esri.extension argument; it currently defaults to ".asc" when 
format="ascii" and to ".flt" when format="binary". (Sorry that the help 
file is not explicit enough regarding the file extensions; will add this 
to the next update.)

Two more remarks on your code:

 >   read.ascii.grid(i)
This simply reads the grid but does nothing else - redundant.

 > prec=1
Slope is calculated in radians (see ?rsaga.slope). So with a 0.1 radian 
increment (the smallest increment that can be represented with prec=1 
digits) you get 0.1 * 180 / pi = 5.7 degree increments on the degree 
scale - you probably want to haver a finer discretization. I would 
recommend prec=3 in the case of slope (and probably prec=6 or 7 for 
curvature attributes).

I hope this helps.

Cheers
  Alex


Tim Sippel wrote:
> I'm using RSAGA (version 0.9-4) to calculate rate of change (slope) on a
> series of .asc files.  I'm getting en error message saying it can't open the
> grid. My code follows:
> 
> library(RSAGA)
> # data directory containing my .asc files to calculate slope on
> wd.in<-"C:\\my.data.dir"
> setwd(wd.in)
> env<-rsaga.env(path="C:\\programs\\saga_vc", cmd="saga_cmd.exe")
> asc.list<-dir(wd.in, pattern='.asc$')
> for (i in asc.list) {
>   read.ascii.grid(i)
>   rsaga.esri.wrapper(fun=rsaga.slope, in.dem=i, method="maxslope",
> in.esri=T, out.esri=T, clean.up=T,
>   out.slope=c(paste("SLOPE",as.character(i),sep="")), env=env,
> esri.workspace=wd.in, format="ascii", georef="corner", prec=1)
>   }
> 
> Here are some of the data files in my directory from my asc.list object
> above:
> 
> asc.list
>  [1] "tmp1_220E-15N2005-03-02.asc"   "tmp10_220E-15N2005-05-13.asc"
> "tmp100_220E-15N2007-05-13.asc" "tmp101_220E-15N2007-05-21.asc"
>  [5] "tmp102_220E-15N2007-05-29.asc" "tmp103_220E-15N2007-06-06.asc"
> "tmp104_220E-15N2007-06-14.asc" "tmp105_220E-15N2007-06-22.asc"
> 
> The error I'm getting is below:
> 
> SAGA CMD 2.0.3
> library path:   C:\programs\saga_vc/modules
> library name:   ta_morphometry
> module name :   Local Morphometry
> author      :   (c) 2001 by O.Conrad
> Load grid: tmp1_220E-15N2005-03-02.asc...
> failed
> error: Grid file could not be opened.
> error: input file [tmp1_220E-15N2005-03-02.asc]
> error: executing module [Local Morphometry]
> 
> Not sure what I've done wrong in calling in the grid files and would
> appreciate advice.
> 
> Best regards,
> 
> Tim Sippel
> University of Auckland
> 
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> 
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-- 
Alexander Brenning
brenning at uwaterloo.ca - T +1-519-888-4567 ext 35783
Department of Geography and Environmental Management
University of Waterloo
200 University Ave. W - Waterloo, ON - Canada N2L 3G1
http://www.fes.uwaterloo.ca/geography/faculty/brenning/