[GRASS-SVN] r59932 - grass/trunk/raster/r.flow

Thu Apr 24 05:31:34 PDT 2014

Author: martinl
Date: 2014-04-24 05:31:34 -0700 (Thu, 24 Apr 2014)
New Revision: 59932

Modified:
   grass/trunk/raster/r.flow/r.flow.html
Log:
r.flow: clean-up the manual


Modified: grass/trunk/raster/r.flow/r.flow.html
===================================================================

--- grass/trunk/raster/r.flow/r.flow.html	2014-04-24 11:56:46 UTC (rev 59931)
+++ grass/trunk/raster/r.flow/r.flow.html	2014-04-24 12:31:34 UTC (rev 59932)
@@ -1,32 +1,40 @@
 <h2>DESCRIPTION</h2>
 
-This program generates flowlines using a combined raster-vector
-approach (see <a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/hmg.rev1.ps">Mitasova and
-Hofierka 1993</a> and <a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/ijgis.html">Mitasova et
-al. 1995</a>) from an input elevation raster map <b>elevation</b>
-(integer or floating point), and optionally an input aspect raster map
-<b>aspect</b> and/or an input barrier raster map <b>barrier</b>. There are
-three possible output maps which can be produced in any combination
-simultaneously: a vector map <b>flowline</b> of flowlines, a raster map
+<em>r.flow</em> generates flowlines using a combined raster-vector
+approach
+(see <a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/hmg.rev1.ps">Mitasova
+and Hofierka 1993</a>
+and <a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/ijgis.html">Mitasova
+et al. 1995</a>) from an input <b>elevation</b> raster map (integer or
+floating point), and optionally an input <b>aspect</b> raster map
+and/or an input <b>barrier</b> raster map.
+
+<p>
+There are three possible output raster maps which can be produced in any
+combination simultaneously: a vector map <b>flowline</b> of flowlines,
+a raster map
 <b>flowlength</b> of flowpath lengths, and a raster map <b>flowaccumulation</b> of flowline
 densities (which are equal upslope contributed areas per unit width, when
 multiplied by resolution).
+
+<h2>NOTES</h2>
+
+Aspect used for input must follow the same rules as aspect computed in
+other modules (see <em><a href="v.surf.rst.html">v.surf.rst</a></em>
+or <em><a href="r.slope.aspect.html">r.slope.aspect</a></em>).
 <p>
-Aspect used for input must follow the same rules as aspect computed
-in other GRASS programs (see <a href="v.surf.rst.html">v.surf.rst</a>
-or <a href="r.slope.aspect.html">r.slope.aspect</a>).
-<p>
-Flowline output is given in a vector map <b>flowline</b>, (flowlines generated
-downhill). The line segments of flowline vectors have endpoints on edges
-of a grid formed by drawing imaginary lines through the centers of the
-cells in the elevation map. Flowlines are generated from each cell downhill
-by default; they can be generated uphill using the flag <b>-u</b>. A flowline
-stops if its next segment would reverse the direction of flow (from up
-to down or vice-versa), cross a barrier, or arrive at a cell with undefined
-elevation or aspect. Another option, <b>skip</b>=val, indicates that only
-the flowlines from every val-th cell are to be included in <b>flowline</b>.
-The default <b>skip</b> is max(1, <rows in elevation>/50, <cols in elevation>/50).
-A high <b>skip</b> usually speeds up processing time and often improves
+Output <b>flowline</b> is generated downhill. The line segments of
+flowline vectors have endpoints on edges of a grid formed by drawing
+imaginary lines through the centers of the cells in the elevation
+map. Flowlines are generated from each cell downhill by default; they
+can be generated uphill using the flag <b>-u</b>. A flowline stops if
+its next segment would reverse the direction of flow (from up to down
+or vice-versa), cross a barrier, or arrive at a cell with undefined
+elevation or aspect. Another option, <b>skip</b>, indicates that
+only the flowlines from every val-th cell are to be included
+in <b>flowline</b>.  The default <b>skip</b> is <tt>max(1, <rows
+in elevation>/50, <cols in elevation>/50)</tt>.  A
+high <b>skip</b> usually speeds up processing time and often improves
 the readability of a visualization of <b>flowline</b>.
 <p>
 Flowpath length output is given in a raster map <b>flowlength</b>. The value
@@ -42,7 +50,7 @@
 
 With the <b>-m</b> flag less memory is used as aspect at each cell is computed
 on the fly. This option incurs a severe performance penalty. If this flag is given,
-the aspect input map (if any) will be ignored.
+the <b>aspect</b> input map (if any) will be ignored.
 
 <!-- doesn't exist
 <p><b>-M</b> Use a fixed size memory and utilize page-swapping to handle
@@ -54,8 +62,7 @@
 The <b>barrier</b> parameter is a raster map name with non-zero
 values representing barriers as input.
 
-
-<h2>NOTES</h2>
+<p>
 For best results, use input elevation maps with high precision units (e.g.,
 centimeters) so that flowlines do not terminate prematurely in flat areas.
 To prevent the creation of tiny flowline segments with imperceivable changes
@@ -63,8 +70,8 @@
 a grid cell is quantized to the exact center of that cell. The maximum
 distance between the intercepts along each axis of a single diagonal segment
 and another segment of 1/2 degree different aspect is taken to be "very
-close" for that axis. Note that this distance (the so-called "quantization
-error") is about 1-2% of the resolution on maps with square cells.
+close" for that axis. Note that this distance (the so-called "quantization
+error") is about 1-2% of the resolution on maps with square cells.
 
 <p>The values in length maps computed using the <b>-u</b> flag represent
 the distances from each cell to an upland flat or singular point. Such
@@ -84,33 +91,37 @@
 water erosion for the computation of the unit stream power based LS factor
 or sediment transport capacity.
 
-<p>The program has been designed for modeling erosion on hillslopes and
-has rather strict conditions for ending flowlines. It is therefore not
-very suitable for the extraction of stream networks or delineation of watersheds
-unless a DEM without pits or flat areas is available
-(<a href=r.fill.dir.html>r.fill.dir</a> can be used to fill pits).
+<p><em>r.flow</em> has been designed for modeling erosion on
+hillslopes and has rather strict conditions for ending flowlines. It
+is therefore not very suitable for the extraction of stream networks
+or delineation of watersheds unless a DEM without pits or flat areas
+is available (<em><a href="r.fill.dir.html">r.fill.dir</a></em> can be
+used to fill pits).
 
 <p> To label the vector flowlines automatically, the user can use
-<a href=v.category.html>v.category</a> (add categories).
+<em><a href="v.category.html">v.category</a></em> (add categories).
 
 <h3>Algorithm background</h3> 
 
-<p>1. Construction of flowlines (slopelines): <em>r.flow</em> uses an original
-vector-grid algorithm which uses an infinite number of directions between
-0.0000... and 360.0000...  and traces the flow as a line (vector) in the
-direction of gradient (rather than from cell to cell in one of the 8
-directions = D-infinity algorithm). They are traced in any direction using
-aspect (so there is no limitation to 8 directions here). The D8 algorithm
-produces zig-zag lines. The value in the outlet is very similar for both
-<em>r.flow</em> and <em>r.flowmd</em> (GRASS 5 only) algorithms (because it is
-essentially the watershed area), however the spatial distribution of flow,
-especially on hillslopes is quite different. It is still a 1D flow routing
-so the dispersal flow is not accurately described, but still better than D8.
+<p>
+<em>r.flow</em> uses an original vector-grid algorithm which uses an
+infinite number of directions between 0.0000... and 360.0000...  and
+traces the flow as a line (vector) in the direction of gradient
+(rather than from cell to cell in one of the 8 directions = D-infinity
+algorithm). They are traced in any direction using aspect (so there is
+no limitation to 8 directions here). The D8 algorithm produces zig-zag
+lines. The value in the outlet is very similar for <em>r.flow</em>
+algorithm (because it is essentially the watershed area), however the
+spatial distribution of flow, especially on hillslopes is quite
+different. It is still a 1D flow routing so the dispersal flow is not
+accurately described, but still better than D8.
 
-<p>2. Computation of contributing areas: <em>r.flow</em> uses a single flow
-algorithm, i.e. all flow is transported to a single cell downslope.
+<p>
+<em>r.flow</em> uses a single flow algorithm, i.e. all flow is
+transported to a single cell downslope.
 
-<h3><b>Differences between <em>r.flow</em> and <em>r.flowmd</em></b></h3>
+<!--
+Differences between <em>r.flow</em> and <em>r.flowmd</em>
 <p>
 <ol>
 
@@ -126,45 +137,54 @@
 
 In conclusion, <em>r.flowmd</em> produces nicer results but is slower and it does not
 support as large data sets as <em>r.flow</em>.
+-->
 
-
 <h3>Diagnostics</h3>
 
-<p>"ERROR: r.flow: " input " file's resolution differs from current" region
-resolution
+<pre>
+Elevation raster map resolution differs from current region resolution
+</pre>
 
-<p>The resolutions of all input files and the current region must match.
+The resolutions of all input raster maps and the current region must
+match (see <em><a href="g.region.html">g.region</a></em>).
 
-<p>"ERROR: r.flow: resolution too unbalanced (" val " x " val ")" The difference
-in length between the two axes of a grid cell is so great that quantization
-error is larger than one of the dimensions. Resample the map and try again.
+<pre>
+Resolution too unbalanced
+</pre>
 
+The difference in length between the two axes of a grid cell is so
+great that quantization error is larger than one of the
+dimensions. Resample the map and try again.
+
 <h2>REFERENCES</h2>
 
-<p>Mitasova, H., L. Mitas, 1993, Interpolation by regularized spline with
+<ul>
+<li>Mitasova, H., L. Mitas, 1993, Interpolation by regularized spline with
 tension : I. Theory and implementation. Mathematical Geology 25, p. 641-655.
 (<a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/lmg.rev1.ps">online</a>)
 
-<p>Mitasova and Hofierka 1993 : Interpolation by Regularized Spline with
+<li>Mitasova and Hofierka 1993 : Interpolation by Regularized Spline with
 Tension: II. Application to Terrain Modeling and Surface Geometry Analysis.
 Mathematical Geology 25(6), 657-669. (<a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/hmg.rev1.ps">online</a>)
 
-<p>Mitasova, H., Mitas, L., Brown, W.M., Gerdes, D.P., Kosinovsky, I.,
+<li>Mitasova, H., Mitas, L., Brown, W.M., Gerdes, D.P., Kosinovsky, I.,
 Baker, T., 1995: Modeling spatially and temporally distributed phenomena:
 New methods and tools for GRASS GIS. International Journal of Geographical
 Information Systems 9(4), 433-446. 
 
-<p>Mitasova, H., J. Hofierka, M. Zlocha, L.R. Iverson, 1996, Modeling
+<li>Mitasova, H., J. Hofierka, M. Zlocha, L.R. Iverson, 1996, Modeling
 topographic potential for erosion and deposition using GIS. Int. Journal of
 Geographical Information Science, 10(5), 629-641. (reply to a comment to
 this paper appears in 1997 in Int. Journal of Geographical Information
 Science, Vol. 11, No. 6)
 
-<p>Mitasova, H.(1993): Surfaces and modeling. Grassclippings (winter and
+<li>Mitasova, H.(1993): Surfaces and modeling. Grassclippings (winter and
 spring) p.18-19.
+</ul>
 
 <h2>SEE ALSO</h2>
 
+<em>
 <a href="r.basins.fill.html">r.basins.fill</a>,
 <a href="r.drain.html">r.drain</a>,
 <a href="r.fill.dir.html">r.fill.dir</a>,
@@ -172,18 +192,18 @@
 <a href="r.watershed.html">r.watershed</a>,
 <a href="v.category.html">v.category</a>,
 <a href="v.to.rast.html">v.to.rast</a>
+</em>
 
-
 <h2>AUTHORS</h2>
 
-<p><i>Original version of program:</i>
-<br>Maros Zlocha and Jaroslav Hofierka, Comenius University, Bratislava,
-Slovakia,
+<i>Original version of program:</i> Maros Zlocha and Jaroslav
+Hofierka, Comenius University, Bratislava, Slovakia
 
-<p><i>The current version of the program (adapted for GRASS5.0)</i>:
-<br>Joshua Caplan, Mark Ruesink, Helena Mitasova, University of Illinois
-at Urbana-Champaign with support from USA CERL.<br>
-<a href="http://www4.ncsu.edu/~hmitaso/gmslab/">GMSL/University of Illinois at 
+<p>
+<i>The current version of the program (adapted for GRASS 5.0)</i>:
+Joshua Caplan, Mark Ruesink, Helena Mitasova, University of Illinois
+at Urbana-Champaign with support from USA CERL. <a href="http://www4.ncsu.edu/~hmitaso/gmslab/">GMSL/University of Illinois at 
 Urbana-Champaign</a>
 
-<p><i>Last changed: $Date$</i>
+<p>
+<i>Last changed: $Date$</i>

