news at max.cecer.army.mil
Tue Mar 30 23:05:17 EST 1993
From: shapiro at zorro.cecer.army.mil (Michael Shapiro)
Subject: Re: topo index
Message-ID: <C4qJCq.L7x at news.cecer.army.mil>
Sender: news at news.cecer.army.mil (Net.Noise owner)
Organization: US Army Corps of Engineers Construction Engineering Research Labs
References: <9303281719.AA04780 at hydro1.geo.duke.edu>
Date: Wed, 31 Mar 1993 04:05:14 GMT
In <9303281719.AA04780 at hydro1.geo.duke.edu> riker at 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)'
>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.
Michael Shapiro shapiro at zorro.cecer.army.mil
U.S. Army CERL (217) 373-7277
P.O. Box 9005
Champaign, Ill. 61826-9005
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