[GRASS-SVN] r54145 - grass/branches/releasebranch_6_4/vector/v.clean
svn_grass at osgeo.org
svn_grass at osgeo.org
Sun Dec 2 13:22:10 PST 2012
Author: neteler
Date: 2012-12-02 13:22:09 -0800 (Sun, 02 Dec 2012)
New Revision: 54145
Modified:
grass/branches/releasebranch_6_4/vector/v.clean/description.html
Log:
documentation more readable
Modified: grass/branches/releasebranch_6_4/vector/v.clean/description.html
===================================================================
--- grass/branches/releasebranch_6_4/vector/v.clean/description.html 2012-12-02 19:41:18 UTC (rev 54144)
+++ grass/branches/releasebranch_6_4/vector/v.clean/description.html 2012-12-02 21:22:09 UTC (rev 54145)
@@ -1,51 +1,57 @@
<h2>DESCRIPTION</h2>
<em>v.clean</em> allows the user to automatically fix topology of vector
-maps.
+maps. Several tools may be listed to be executed sequentially. In this
+case, also the threshold parameter requires several values to be listed
+accordingly. An error map is optionally written which stores the errorneous
+geometries.
<h3>Break lines/boundaries</h3>
<em>tool=break</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
+The <em>break</em> tool breaks lines/boundaries at intersections and it
+<!-- TODO: what is a collapsed loop?? self-intersecting? -->
+also breaks lines/boundaries forming a collapsed loop.
+<!-- TODO: this example is a complete mystery: -->
+For example, 0.0;1.0;0.0 is broken at 1.0.
<p>
-The <em>break</em> tool breaks lines/boundaries at intersections and also
-breaks lines/boundaries forming a collapsed loop, for example 0.0;1.0;0.0
-is broken at 1.0.
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
<p>
-Breaking lines should be followed by removing duplicates, e.g.
+Hint: Breaking lines should be followed by removing duplicates, e.g.
<em>v.clean tool=break,rmdupl</em>.
<h3>Remove duplicate geometry features</h3>
<em>tool=rmdupl</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
The <em>rmdupl</em> tool removes geometry features with identical
coordinates. Categories are merged. If a point and a centroid have
identical coordinates, one of them will be removed if both points and
-centroids are selected with <em>v.clean type=point,centroid</em>. The
-same applies for lines and boundaries.
+centroids are selected with <em>v.clean ... type=point,centroid</em>.
+The same applies for lines and boundaries.
<p>
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
+<p>
The <em>rmdupl</em> tool should be used after breaking lines and
breaking polygons.
<h3>Remove dangles or change boundary dangles to type line</h3>
<em>tool=rmdangle</em> and <em>tool=chdangle</em>
<p>
-Threshold gives maximum line/boundary length in map units, degrees for
-latlon. Dangles shorter than <em>thresh</em> are removed sequentially.
-All dangles will be removed if <em>thresh</em> < 0.
-<p>
A line/boundary is considered to be a dangle if no other line of given
<em>type</em> is on at least one end node. If a dangle is formed by
several lines, such a string of lines is taken as one dangle and line
lengths are summarized. The <em>rmdangle</em> tool deletes a dangle if
-the (combined) length is shorter than <em>thres</em> or <em>thres</em>
+the (combined) length is shorter than <em>thresh</em> or <em>thresh</em>
< 0. If the combined length is larger than <em>thresh</em>, nothing
is deleted.
<p>
+Threshold has to be given as maximum line/boundary length in map units;
+for latitude-longitude locations in degree. Dangles shorter than
+<em>thresh</em> are removed sequentially. All dangles will be removed if
+<em>thresh</em> < 0.
+<p>
With <em>thresh</em> < 0, only closed loops and lines connecting
loops will remain. This is useful to remove all incorrect boundaries
after other cleaning operations with <em>thres</em> is < 0. Areas can
@@ -53,18 +59,17 @@
<p>
To preferentially remove shortest dangles first, a first pass with a
small <em>thresh</em> value can be followed by subsequent passes with
-increasing <em>thresh</em> values.
+higher <em>thresh</em> values. This can be done as one <em>v.clean</em>
+job by listing the tool several times and by defining a list of increasing
+<em>thresh</em> values.
<p>
The <em>chdangle</em> tool is similar to the <em>rmdangle</em> tool, but
works only on boundaries and changes dangling boundaries to lines
-instead of removing dangles.
+instead of removing them.
<h3>Remove or change bridges connecting an area and an island or two islands</h3>
<em>tool=rmbridge</em> and <em>tool=chbridge</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
A bridge is an area type connection of an island (polygon in a polygon)
to the outer polygon. This is topologically incorrect (but OGC Simple
Features allow it). The <em>rmbridge</em> tool removes bridges and the
@@ -84,39 +89,40 @@
</pre></div>
<p>
Islands and areas must be already clean, i.e. without dangles or small
-angles, e.g. <em>v.clean type=boundary tool=rmdangle,rmsa,break,rmdupl,rmbridge
+angles, e.g.
+<em>v.clean ... type=boundary tool=rmdangle,rmsa,break,rmdupl,rmbridge
thresh=-1,0,0,0,0</em>.
+<p>
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
<h3>Snap lines to vertex in threshold</h3>
<em>tool=snap</em>
<p>
-Threshold gives maximum distance to another vertex in map units,
-degrees for latlon.
-<p>
The <em>snap</em> tool snaps vertices to another vertex not farther away
than <em>thresh</em>. If there is no other vertex within <em>thresh</em>,
no snapping will be done. The <em>type</em> option can have a strong
influence on the result. A too large threshold and <em>type=boundary</em>
can severely damage area topology, beyond repair.
<p>
+Threshold gives maximum distance to another vertex in map units,
+for latitude-longitude locations in degree.
+<p>
Snapped boundaries may need to be cleaned with <em>break,rmdupl,rmsa</em>.
<h3>Remove duplicate area centroids</h3>
<em>tool=rmdac</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
The <em>rmdac</em> tool removes duplicate area centroids that can result
from deleting boundaries.
+<p>
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
<h3>Break (topologically clean) areas (imported from a non topological
format like ShapeFile)</h3>
<em>tool=bpol</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
The <em>bpol</em> tool breaks boundaries on each point shared between 2
and more areas where angles of boundary segments are different and on
all boundary nodes (start and end points of each boundary). The
@@ -124,6 +130,9 @@
does not break collapsed loops. The <em>bpol</em> tool is faster than
the <em>break</em> tool but needs more memory.
<p>
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
+<p>
The <em>bpol</em> tool should be followed by <em>rmdupl</em>.
<h3>Remove vertices in threshold from lines and boundaries</h3>
@@ -132,40 +141,41 @@
The <em>prune</em> tool simplifies lines and boundaries by removing
vertices according to threshold. This tool preserves area topology,
areas are never deleted and centroid attachment is never changed.
-<em><a href=v.generalize.html>v.generalize</a></em> offers much more
+<em><a href="v.generalize.html">v.generalize</a></em> offers much more
functionality for line simplification but does not preserve area
topology.
<h3>Remove small areas</h3>
<em>tool=rmarea</em>
<p>
-Threshold gives area size in map units, square meters for latlon.
-<p>
The <em>rmarea</em> tool removes all areas <= <em>thresh</em>. The
longest boundary with an adjacent area is removed or all boundaries if
there is no adjacent area. Area categories are not combined when a small
area is merged with a larger area.
+<p>
+Threshold gives area size in map units, for latitude-longitude locations
+in square meters.
<h3>Remove all lines or boundaries of zero length</h3>
<em>tool=rmline</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
The <em>rmline</em> tool removes all lines or boundaries of zero length
that may have resulted from other cleaning operations. Zero length
boundaries are redundant and do not influence area topology.
+<p>
+Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0)
+if <em>v.clean</em> is run with several tools.
<h3>Remove small angles between lines at nodes</h3>
<em>tool=rmsa</em>
<p>
-Threshold does not apply, use dummy value if <em>v.clean</em> is
-run with several tools.
-<p>
The <em>rmsa</em> tool only concerns angles which are so small that the
calculated angle is 0. The following figure should help demonstrate what
the tool does.
<p>
+Threshold does not apply, use dummy value if <em>v.clean</em> is
+run with several tools.
+<p>
<table><tr><td>
<img src="v_clean_rmsa.png" border=1>
</td></tr>
@@ -193,7 +203,7 @@
v.clean input=testmap output=cleanmap tool=snap thresh=1
</pre></div>
-<h3>Cleaning OGR imported data (Simple Feature data)</h3>
+<h3>Cleaning OGR imported data (Simple Feature data) such as SHAPE file</h3>
The import of areas with <em><a href="v.in.ogr.html">v.in.ogr</a> -c</em>
(no cleaning) requires a subsequent run of <em>v.clean</em> to update
@@ -256,7 +266,8 @@
<h3>Repeatedly remove dangling lines up to 50m length</h3>
<div class="code"><pre>
-v.clean input=testmap output=cleanmap type=line tool=rmdangle,rmdangle,rmdangle,rmdangle thresh=5,10,20,50
+v.clean input=testmap output=cleanmap type=line \
+ tool=rmdangle,rmdangle,rmdangle,rmdangle thresh=5,10,20,50
</pre></div>
<h2>SEE ALSO</h2>
@@ -272,6 +283,6 @@
David Gerdes, U.S. Army Construction Engineering Research Laboratory<br>
Radim Blazek, ITC-irst, Trento, Italy<br>
-Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy<br>
+Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy
<p><i>Last changed: $Date$</i>
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