problems with r.mapcalc

Malcolm Williamson malcolm at
Tue Dec 13 13:11:26 EST 1994

> Hello.  I have used r.slope.aspect to generate a raster map of 
> slopes.  The map has labeled each point with slope in degrees.
> I would like to get slope as the tangent of the degrees.  I used
> r.mapcalc, and used the equation:
> tan.0 = tan(@slope.0)
> where tan.0 is my output map and slope.0 is the raster map with
> slopes.  However, I get tangent values equal to either zero or
> one, and no fractional values.  Can anyone help?
> John Stamm

Remember, GRASS does not support floating point values in raster layers!
Therefore, you must multiply by some factor. For example:

	tan.0 = tan(@slope.0) * 100.0

Hope this works for you.
Malcolm D. Williamson - GIS Specialist           E-mail: malcolm at
Center for Advanced Spatial Technologies      Telephone: (501) 575-6159
Ozark Rm. 12                                        Fax: (501) 575-3846 
University of Arkansas              
Fayetteville, AR 72701

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