[GRASS-SVN] r59393 - grass/trunk/raster/r.stream.extract
svn_grass at osgeo.org
svn_grass at osgeo.org
Thu Mar 27 03:04:08 PDT 2014
Author: martinl
Date: 2014-03-27 03:04:08 -0700 (Thu, 27 Mar 2014)
New Revision: 59393
Modified:
grass/trunk/raster/r.stream.extract/main.c
grass/trunk/raster/r.stream.extract/r.stream.extract.html
Log:
r.stream.extract: follow manual rules (bold parameters, linked modules)
Modified: grass/trunk/raster/r.stream.extract/main.c
===================================================================
--- grass/trunk/raster/r.stream.extract/main.c 2014-03-27 09:47:26 UTC (rev 59392)
+++ grass/trunk/raster/r.stream.extract/main.c 2014-03-27 10:04:08 UTC (rev 59393)
@@ -6,7 +6,7 @@
* PURPOSE: Hydrological analysis
* Extracts stream networks from accumulation raster with
* given threshold
- * COPYRIGHT: (C) 1999-2009 by the GRASS Development Team
+ * COPYRIGHT: (C) 1999-2014 by the GRASS Development Team
*
* This program is free software under the GNU General Public
* License (>=v2). Read the file COPYING that comes with GRASS
Modified: grass/trunk/raster/r.stream.extract/r.stream.extract.html
===================================================================
--- grass/trunk/raster/r.stream.extract/r.stream.extract.html 2014-03-27 09:47:26 UTC (rev 59392)
+++ grass/trunk/raster/r.stream.extract/r.stream.extract.html 2014-03-27 10:04:08 UTC (rev 59393)
@@ -1,37 +1,37 @@
<h2>DESCRIPTION</h2>
<em>r.stream.extract</em> extracts streams in both raster and vector
-format from a required input <em>elevation</em> map and optional input
-<em>accumulation</em> map.
+format from a required input <b>elevation</b> map and optional input
+<b>accumulation</b> map.
<h2>OPTIONS</h2>
<dl>
-<dt><em>elevation</em>
+<dt><b>elevation</b>
<dd>Input map, required: Elevation on which the entire analysis is based.
NULL (nodata) cells are ignored, zero and negative values are valid
elevation data. Gaps in the elevation map that are located within the
area of interest must be filled beforehand, e.g. with
-<em>r.fillnulls</em>, to avoid distortions.
+<em><a href="r.fillnulls.html">r.fillnulls</a></em>, to avoid distortions.
<p>
-<dt><em>accumulation</em>
+<dt><b>accumulation</b>
<dd>Input map, optional: Accumulation values of the provided
-<em>accumulation</em> map are used and not calculated from the input
-<em>elevation</em> map. If <em>accumulation</em> is given,
-<em>elevation</em> must be exactly the same map used to calculate
-<em>accumulation</em>. If <em>accumulation</em> was calculated with
-<a href="r.terraflow.html">r.terraflow</a>, the filled elevation output
+<b>accumulation</b> map are used and not calculated from the input
+<b>elevation</b> map. If <b>accumulation</b> is given,
+<b>elevation</b> must be exactly the same map used to calculate
+<b>accumulation</b>. If <b>accumulation</b> was calculated with
+<em><a href="r.terraflow.html">r.terraflow</a></em>, the filled elevation output
of r.terraflow must be used. Further on, the current region should be
-aligned to the <em>accumulation map</em>. Flow direction is
-first calculated from <em>elevation</em> and then adjusted to
-<em>accumulation</em>. It is not necessary to provide <em>accumulation</em>
+aligned to the <b>accumulation</b> map. Flow direction is
+first calculated from <b>elevation</b> and then adjusted to
+<b>accumulation</b>. It is not necessary to provide <b>accumulation</b>
as the number of cells, it can also be the optionally adjusted or
weighed total contributing area in square meters or any other unit.
When an original flow accumulation map is adjusted or weighed, the
adjustment or weighing should not convert valid accumulation values to
NULL (nodata) values.
<p>
-<dt><em>depression</em>
+<dt><b>depression</b>
<dd>Input map, optional: All non-NULL and non-zero cells will be regarded
as real depressions. Streams will not be routed out of depressions. If an
area is marked as depression but the elevation model has no depression
@@ -41,42 +41,42 @@
the indicated depressions. It is recommended to use internally computed
flow accumulation if a depression map is provided.
<p>
-<dt><em>threshold</em>
-<dd>Required: <em>threshold</em> for stream initiation by overland flow:
+<dt><b>threshold</b>
+<dd>Required: <b>threshold</b> for stream initiation by overland flow:
the minumum (optionally modifed) flow accumulation value that will initiate
a new stream. If Montgomery's method for channel initiation is used, the
cell value of the accumulation input map is multiplied by
-(tan(local slope))<sup>mexp</sup> and then compared to <em>threshold</em>.
+(tan(local slope))<sup>mexp</sup> and then compared to <b>threshold</b>.
<p>
-<dt><em>d8cut</em>
+<dt><b>d8cut</b>
<dd>Minimum amount of overland flow (accumulation) when SFD (D8) will be
used instead of MFD (FD8) to calculate flow accumulation. Only applies
if no accumulation map is provided. Setting to 0 disables MFD completely.
<p>
-<dt><em>mexp</em>
+<dt><b>mexp</b>
<dd>Use the method of Montgomery and Foufoula-Georgiou (1993) to
-initiate a stream with exponent <em>mexp</em>. The cell value of the
+initiate a stream with exponent <b>mexp</b>. The cell value of the
accumulation input map is multiplied by (tan(local slope))<sup>mexp</sup>
-and then compared to <em>threshold</em>. If threshold is reached or
+and then compared to <b>threshold</b>. If threshold is reached or
exceeded, a new stream is initiated. The default value 0 disables
Montgomery. Montgomery and Foufoula-Georgiou (1993) generally recommend
-to use 2.0 as exponent. <em>mexp</em> values closer to 0 will produce
+to use 2.0 as exponent. <b>mexp</b> values closer to 0 will produce
streams more similar to streams extracted with Montgomery disabled.
-Larger <em>mexp</em> values decrease the number of streams in flat areas
-and increase the number of streams in steep areas. If <em>weight</em> is
+Larger <b>mexp</b> values decrease the number of streams in flat areas
+and increase the number of streams in steep areas. If <b>weight</b> is
given, the weight is applied first.
<p>
-<dt><em>stream_length</em>
+<dt><b>stream_length</b>
<dd>Minimum stream length in number of cells for first-order (head/spring)
stream segments. All first-order stream segments shorter than
-<em>stream_length</em> will be deleted.
+<b>stream_length</b> will be deleted.
<p>
-<dt><em>stream_rast</em>
+<dt><b>stream_rast</b>
<dd>Output raster map with extracted streams. Cell values encode a
unique ID for each stream segment.
<p>
-<dt><em>stream_vect</em>
+<dt><b>stream_vect</b>
<dd>Output vector map with extracted stream segments and points. Points
are written at the start location of each stream segment and at the
outlet of a stream network. In layer 1, categories are unique IDs,
@@ -89,7 +89,7 @@
points. Points with category 1 = intermediate in layer 2 are at the
location of confluences.
<p>
-<dt><em>direction</em>
+<dt><b>direction</b>
<dd>Output raster map with flow direction for all non-NULL cells in
input elevation. Flow direction is of D8 type with a range of 1 to 8.
Multiplying values with 45 gives degrees CCW from East. Flow direction
@@ -100,62 +100,68 @@
<h2>NOTES</h2>
<h4>Stream extraction</h4>
+
If no accumulation input map is provided, flow accumulation is
determined with a hydrological anaylsis similar to
-<a href="r.watershed.html">r.watershed</a>. The algorithm is
+<em><a href="r.watershed.html">r.watershed</a></em>. The algorithm is
MFD (FD8) after Holmgren 1994, as for
-<a href="r.watershed.html">r.watershed</a>. The <em>threshold</em>
+<em><a href="r.watershed.html">r.watershed</a></em>. The <b>threshold</b>
option determines the number of streams and detail of stream networks.
-Whenever flow accumulation reaches <em>threshold</em>, a new stream is
+Whenever flow accumulation reaches <b>threshold</b>, a new stream is
started and traced downstream to its outlet point. As for
-<a href="r.watershed.html">r.watershed</a>, flow accumulation is
+<em><a href="r.watershed.html">r.watershed</a></em>, flow accumulation is
calculated as the number of cells draining through a cell.
<h4>Weighed flow accumulation</h4>
+
Flow accumulation can be calculated first, e.g. with
-<a href="r.watershed.html">r.watershed</a>, and then modified before
+<em><a href="r.watershed.html">r.watershed</a></em>, and then modified before
using it as input for <em>r.stream.extract</em>. In its general form, a
weighed accumulation map is generated by first creating a weighing map
and then multiplying the accumulation map with the weighing map using
-<a href="r.mapcalc.html">r.mapcalc</a>. It is highly recommended to
+<em><a href="r.mapcalc.html">r.mapcalc</a></em>. It is highly recommended to
evaluate the weighed flow accumulation map first, before using it as
input for <em>r.stream.extract</em>.
<p>
This allows e.g. to decrease the number of streams in dry areas and
-increase the number of streams in wet areas by setting <em>weight</em>
+increase the number of streams in wet areas by setting <b>weight</b>
to smaller than 1 in dry areas and larger than 1 in wet areas.
<p>
Another possibility is to restrict channel initiation to valleys
determined from terrain morphology. Valleys can be determined with
-<a href="r.param.scale.html">r.param.scale</a> param=crosc
+<em><a href="r.param.scale.html">r.param.scale</a></em> <tt>param=crosc</tt>
(cross-sectional or tangential curvature). Curvature values < 0
indicate concave features, i.e. valleys. The size of the processing
window determines whether narrow or broad valleys will be identified
(See example below).
<h4>Defining a region of interest</h4>
+
The stream extraction procedure can be restricted to a certain region of
interest, e.g. a subbasin, by setting the computational region with
-<em>g.region</em> and/or creating a MASK. Such region of interest should
+<em><a href="g.region.html">g.region</a></em> and/or creating a MASK. Such region of interest should
be a complete catchment area, complete in the sense that the complete
area upstream of an outlet point is included and buffered with at least
one cell.
<h4>Stream output</h4>
-The <em>stream_rast</em> output raster and vector contains stream
-segments with unique IDs. Note that these IDs are different from the IDs
-assigned by <a href="r.watershed.html">r.watershed</a>. The vector
+
+The <b>stream_rast</b> output raster and vector contains stream
+segments with unique IDs. Note that these IDs are different from the
+IDs assigned
+by <em><a href="r.watershed.html">r.watershed</a></em>. The vector
output also contains points at the location of the start of a stream
segment, at confluences and at stream network outlet locations.
<p>
<h2>EXAMPLE</h2>
-This example is based on the elevation map <em>elev_ned_30m</em> in the
+
+This example is based on the elevation map "elev_ned_30m" in the
North Carolina sample dataset and uses valleys determined with
-<a href="r.param.scale.html">r.param.scale</a> to weigh an accumulation
-map produced with <a href="r.watershed.html">r.watershed</a>.
+<em><a href="r.param.scale.html">r.param.scale</a></em> to weigh an accumulation
+map produced with <em><a href="r.watershed.html">r.watershed</a></em>.
-<pre>
+<div class="code"><pre>
# set region
g.region -p rast=elev_ned_30m at PERMANENT
@@ -199,10 +205,29 @@
accumulation=elev_ned_30m.acc \
threshold=1000 \
stream_rast=elev_ned_30m.streams.noweight
-</pre>
+</pre></div>
Now display both stream maps and decide which one is more realistic.
+<h2>REFERENCES</h2>
+
+<ul>
+<li>Ehlschlaeger, C. (1989). <i>Using the A<sup>T</sup> Search
+Algorithm to Develop Hydrologic Models from Digital Elevation
+Data</i>,
+<b>Proceedings of International Geographic Information Systems (IGIS)
+Symposium '89</b>, pp 275-281 (Baltimore, MD, 18-19 March
+1989). URL: <a href="http://faculty.wiu.edu/CR-Ehlschlaeger2/older/IGIS/paper.html">
+http://faculty.wiu.edu/CR-Ehlschlaeger2/older/IGIS/paper.html</a></li>
+<li>Holmgren, P. (1994). <i>Multiple flow direction algorithms for
+runoff modelling in grid based elevation models: An empirical
+evaluation.</i>
+<b>Hydrological Processes</b> Vol 8(4), pp 327-334. DOI: <a href="http://dx.doi.org/10.1002/hyp.3360080405">10.1002/hyp.3360080405</a></li>
+<li>Montgomery, D.R., Foufoula-Georgiou, E. (1993). <i>Channel network source
+representation using digital elevation models.</i>
+<b>Water Resources Research</b> Vol 29(12), pp 3925-3934.</li>
+</ul>
+
<h2>SEE ALSO</h2>
<em>
@@ -214,25 +239,6 @@
<a href="r.to.vect.html">r.to.vect</a>
</em>
-<h2>REFERENCES</h2>
-Ehlschlaeger, C. (1989). <i>Using the A<sup>T</sup> Search Algorithm
-to Develop Hydrologic Models from Digital Elevation Data</i>,
-<b>Proceedings of International Geographic Information Systems (IGIS)
-Symposium '89</b>, pp 275-281 (Baltimore, MD, 18-19 March 1989).<br>
-URL: <a href="http://faculty.wiu.edu/CR-Ehlschlaeger2/older/IGIS/paper.html">
-http://faculty.wiu.edu/CR-Ehlschlaeger2/older/IGIS/paper.html</a>
-
-<p>
-Holmgren, P. (1994). <i>Multiple flow direction algorithms for runoff
-modelling in grid based elevation models: An empirical evaluation.</i>
-<b>Hydrological Processes</b> Vol 8(4), pp 327-334.<br>
-DOI: <a href="http://dx.doi.org/10.1002/hyp.3360080405">10.1002/hyp.3360080405</a>
-
-<p>
-Montgomery, D.R., Foufoula-Georgiou, E. (1993). <i>Channel network source
-representation using digital elevation models.</i>
-<b>Water Resources Research</b> Vol 29(12), pp 3925-3934.
-
<h2>AUTHOR</h2>
Markus Metz
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