Newsgroups: info.grass.user
Path: zorro.cecer.army.mil!shapiro
From: shapiro@zorro.cecer.army.mil (Michael Shapiro)
Subject: Re: topo index
Message-ID: <C4qJCq.L7x@news.cecer.army.mil>
Sender: news@news.cecer.army.mil (Net.Noise owner)
Organization: US Army Corps of Engineers Construction Engineering Research Labs
References: <9303281719.AA04780@hydro1.geo.duke.edu>
Date: Wed, 31 Mar 1993 04:05:14 GMT
Lines: 22
In <9303281719.AA04780@hydro1.geo.duke.edu> riker@hydro1.geo.duke.edu (Dan Riker) writes:
If you are using r.mapcalc, you have to bve careful about integer vs floats.
The expression a/tanB would be integer divison since a and tanB are maps
(which are taken to be integer) and trucncated to integer before passed to ln().
The the relsuts of ln are again rounded to integer so that the result can
be sore in a raster map (which hold integers only).
Try r.mapcalc 'x = 1000 * ln(float(a)/tanB)'
Hello there,
I am still trying to determine the topographic index ln(a/tanB) and i do have some values. they seem to me to be strange, in that there is a bimodal distribution, with peaks at 17 and 0, while the lows are at 21(the highest value) and 13. Is this a common thing for rugged topography?
If not, any suggestions as to what I am doing wrong?
I think that it would really help if i had an example set of data, so if anyone could supply it I would be most appreciative.
Thanks,
Dan Riker
Duke University
--
Michael Shapiro shapiro@zorro.cecer.army.mil
U.S. Army CERL (217) 373-7277
P.O. Box 9005
Champaign, Ill. 61826-9005