.TH r.slope
.SH NAME
\fIr.slope\fR \- Generates raster map layer of slope 
from a raster map layer of true elevation values.
.br
.I (GRASS Raster Program)
.SH SYNOPSIS
\fBr.slope\fR
.br
\fBr.slope help\fR
.br
\fBr.slope \fR[\fB-q\fR] \fBelevation\*=\fIname \fBslope\*=\fIname\fR 
.SH DESCRIPTION
\fIr.slope\fR generates a raster map layer of slope 
from a raster map layer of true elevation values.
The user must specify the input elevation file name
and an output file name to contain the slope data.

The program will be run non-interactively if the user specifies
program inputs and any desired options on the command line, using the form
.LP
.RS
\fBr.slope \fR[\fB-q\fR] \fBelevation\*=\fIname \fBslope\*=\fIname\fR 
.RE
.LP
If the user runs:
.RS
\fBr.slope\fR
.RE
.LP
without command line arguments, the program will prompt the user
for flag settings and parameter values.

.LP
\fBFlags:\fR
.IP \fB-q\fR 18
Run quietly, and suppress the printing of information on program operations
during execution.
.LP
\fBParameters:\fR
.IP \fBelevation\*=\fIname\fR 18
Name of the raster map layer of true elevation values to be used as input.
.IP \fBslope\*=\fIname\fR 18
Name of a raster map layer of slope values created from the elevation map.
.LP
Resulting raster map layer of slope is named by the user
and placed in the current mapset.
.SH ELEVATION RASTER MAP
The raster elevation map layer specified by the user must contain
true elevation values, \fInot\fR rescaled or categorized data.
.SH SLOPE RASTER MAP
The resulting raster slope map layer will contain slope values,
stated in percent multiplied by 10. For example, a category
value of 15 would indicate a slope of 1.5%.
The category file, but not the color table, is generated by
\fIr.slope\fR for the raster slope map layer.
.RE
.SH NOTES
This program is really a stripped-down modification of the
\fIr.slope.aspect\fR program written by Michael Shapiro and
Marjorie Larson of U.S. Army Construction Engineering Research Laboratory,
and was created with a particular purpose in mind. 
The primary differences are 1) only slope is calculated (no aspect)
2) slope is calculated in percent multiplied by 10, not in degrees.

The region is set to that of the elevation file, and there is
no option to align as there is in \fIr.slope.aspect\fR.

The current mask, if set, is ignored.

The algorithm used to determine slope uses a 3x3 neighborhood
around each cell in the elevation file.
Thus, it is not possible to determine slope for the cells
adjacent to the edges in the elevation map layer.
These cells are assigned a value of 0 (zero).
.SH WARNING
Elevations of zero (as well as below sea level elevations) are valid.
This means that areas assigned category value 0 may have one of two possible
meanings:  they may either be areas of "no data" or areas having 0 elevation.
Also, if all elevation values in the 3x3 neighborhood are the same,
the slope will also be 0.
.SH SEE ALSO
.I r.slope.aspect,
.I r.mapcalc,
.I r.neighbors,
.I r.reclass,
.I r.rescale
.SH "AUTHORS"
Chris Rewerts, Agricultural Engineering, Purdue University
.br
Raghaven Srinivasan, Agricultural Engineering, Purdue University
