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<h2>DESCRIPTION</h2>
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-<b>r.slope.aspect </b>generates raster maps of slope, aspect, curvatures and
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+<em>r.slope.aspect</em> generates raster maps of slope, aspect, curvatures and
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first and second order partial derivatives from a raster map of true
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-elevation values. The user must specify the input <i>elevation</i> file name
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-and at least one output file name. The user can also specify the
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-<i>format</i> for slope (degrees, percent; default=degrees), and the
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-<i>zfactor</i>: multiplicative factor to convert elevation units to meters;
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+elevation values. The user must specify the input <b>elevation</b> raster map
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+and at least one output raster maps. The user can also specify the
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+<b>format</b> for slope (degrees, percent; default=degrees), and the
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+<b>zfactor</b>: multiplicative factor to convert elevation units to meters;
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(default 1.0).
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+
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<p>
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-The <i>elevation</i> input raster map specified by the user must contain true
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-elevation values, <b>not</b> rescaled or categorized data. If the elevation
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+The <b>elevation</b> input raster map specified by the user must contain true
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+elevation values, <em>not</em> rescaled or categorized data. If the elevation
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values are in feet or other units than meters (with a conversion factor
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<i>meters:</i>, defined in PROJ_UNITS), they must be converted to meters using
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-the parameter <i>zfactor</i>.
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+the parameter <b>zfactor</b>.
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+
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<p>
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-The <i>aspect</i> output raster map indicates the direction that slopes are
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+The <b>aspect</b> output raster map indicates the direction that slopes are
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facing. The aspect categories represent the number degrees of east. Category
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-and color table files are also generated for the aspect map layer. The aspect
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+and color table files are also generated for the aspect raster map. The aspect
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categories represent the number degrees of east and they increase
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counterclockwise: 90deg is North, 180 is West, 270 is South 360 is East. The
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aspect value 0 is used to indicate undefined aspect in flat areas with slope=0.
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+
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<p>
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-The <i>slope</i> output raster map contains slope values, stated in degrees of
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-inclination from the horizontal if <i>format</i>=degrees option (the default)
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-is chosen, and in percent rise if <i>format</i>=percent option is chosen.
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+The <b>slope</b> output raster map contains slope values, stated in degrees of
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+inclination from the horizontal if <b>format</b>=degrees option (the default)
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+is chosen, and in percent rise if <b>format</b>=percent option is chosen.
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Category and color table files are generated.
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+
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<p>
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Profile and tangential curvatures are the curvatures in the direction of
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steepest slope and in the direction of the contour tangent respectively. The
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@@ -84,7 +88,7 @@ are negative.
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<p>For some applications, the user will wish to use a reclassified raster map
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of slope that groups slope values into ranges of slope. This can be done using
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-<i><a href="r.reclass.html">r.reclass</a></i>. An example of a useful
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+<em><a href="r.reclass.html">r.reclass</a></em>. An example of a useful
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reclassification is given below:
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<div class="code"><pre> category range category labels
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(in degrees) (in percent)
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@@ -114,23 +118,23 @@ reclassification is given below:
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<h2>NOTES</h2>
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-To ensure that the raster elevation map layer is not inappropriately resampled,
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+To ensure that the raster elevation map is not inappropriately resampled,
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the settings for the current region are modified slightly (for the execution
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of the program only): the resolution is set to match the resolution of
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-the elevation map and the edges of the region (i.e. the north, south, east
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+the elevation raster map and the edges of the region (i.e. the north, south, east
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and west) are shifted, if necessary, to line up along edges of the nearest
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-cells in the elevation map. If the user really wants the elevation map
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-resampled to the current region resolution, the -a flag should be specified.
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+cells in the elevation map. If the user really wants the raster elevation map
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+resampled to the current region resolution, the <b>-a</b> flag should be specified.
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<p>
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The current mask is ignored.
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<p>
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The algorithm used to determine slope and aspect uses a 3x3 neighborhood
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-around each cell in the elevation file. Thus, it is not possible to determine
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+around each cell in the raster elevation map. Thus, it is not possible to determine
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slope and aspect for the cells adjacent to the edges in the elevation map
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layer. These cells are assigned a "zero slope" value (category 0) in both
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-the slope and aspect raster map layers.
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+the slope and aspect raster maps.
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<p>
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Horn's formula is used to find the first order derivatives in x and y directions.
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@@ -145,9 +149,9 @@ When working with floating point elevation models, no such aspect bias occurs.
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Because most cells with a very small slope end up having category 0,
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45, ..., 360, it is sometimes possible to reduce the bias in these directions
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by filtering out the aspect in areas where the terrain is almost flat. A new
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-option <i>min_slp_allowed</i> was added to specify the minimum slope for which
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+option <b>min_slp_allowed</b> was added to specify the minimum slope for which
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aspect is computed. The aspect for all cells with slope <
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-<i>min_slp_allowed</i> is set to <b>null</b>.
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+<b>min_slp_allowed</b> is set to <i>null</i> (no-data).
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<h2>REFERENCE</h2>
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@@ -166,13 +170,16 @@ Developments in Soil Science, vol. 33, Elsevier, 387-410 pp,
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<h2>SEE ALSO</h2>
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-<em><a href="r.mapcalc.html">r.mapcalc</a></em>,
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-<em><a href="r.neighbors.html">r.neighbors</a></em>,
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-<em><a href="r.reclass.html">r.reclass</a></em>,
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-<em><a href="r.rescale.html">r.rescale</a></em>
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+<em>
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+ <a href="r.mapcalc.html">r.mapcalc</a>,
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+ <a href="r.neighbors.html">r.neighbors</a>,
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+ <a href="r.reclass.html">r.reclass</a>,
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+ <a href="r.rescale.html">r.rescale</a>
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+</em>
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<h2>AUTHORS</h2>
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+
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Michael Shapiro, U.S.Army Construction Engineering Research Laboratory<br>
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Olga Waupotitsch, U.S.Army Construction Engineering Research Laboratory
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