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       v.clean  - Toolset for cleaning topology of vector map.


       vector, topology


       v.clean help
       v.clean    [-b]    input=name   output=name    [type=string[,string,...]]     [error=name]
       tool=string[,string,...]     [thresh=float[,float,...]]      [--overwrite]     [--verbose]

           Don't build topology for the output vector

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input vector map

           Name for output vector map

           Feature type
           Options: point,line,boundary,centroid,area,face,kernel
           Default: point,line,boundary,centroid,area

           Name of output map where errors are written

           Cleaning tool
           break: break lines at each intersection
           snap: snap lines to vertex in threshold
           rmdangle: remove dangles, threshold ignored if < 0
           chdangle:  change the type of boundary dangle to line, threshold ignored if < 0, input
           line type is ignored
           rmbridge: remove bridges connecting area and island or 2 islands
           chbridge: change the type of bridges connecting area and  island  or  2  islands  from
           boundary to line
           rmdupl: remove duplicate geometry features (pay attention to categories!)
           rmdac: remove duplicate area centroids ('type' option ignored)
           bpol: break (topologically clean) polygons (imported from non topological format, like
           ShapeFile). Boundaries are broken on each point shared between  2  and  more  polygons
           where angles of segments are different
           prune: remove vertices in threshold from lines and boundaries, boundary is pruned only
           if topology is not damaged (new intersection, changed attachment of  centroid),  first
           and last segment of the boundary is never changed
           rmarea: remove small areas, the longest boundary with adjacent area is removed
           rmline: remove all lines or boundaries of zero length, threshold is ignored
           rmsa: remove small angles between lines at nodes

           Threshold in map units, one value for each tool (default: 0.0[,0.0,...])


       v.clean allows the user to automatically fix topology of vector 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.

   Break lines/boundaries

       The  break  tool  breaks  lines/boundaries   at   intersections   and   it   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 v.clean is
       run with several tools.

       Hint:  Breaking  lines  should  be  followed  by  removing   duplicates,   e.g.    v.clean

   Remove duplicate geometry features

       The  rmdupl  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 v.clean ... type=point,centroid.  The  same
       applies for lines and boundaries.

       Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0) if  v.clean  is
       run with several tools.

       The rmdupl tool should be used after breaking lines and breaking polygons.

   Remove dangles or change boundary dangles to type line
       tool=rmdangle and tool=chdangle

       A line/boundary is considered to be a dangle if no other line of given type 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 rmdangle tool deletes a dangle if the
       (combined) length is shorter than thresh or thresh < 0. If the combined length  is  larger
       than thresh, nothing is deleted.

       Threshold  has  to  be  given  as maximum line/boundary length in map units; for latitude-
       longitude locations in degree. Dangles shorter than thresh are removed  sequentially.  All
       dangles will be removed if thresh < 0.

       With  thresh < 0, only closed loops and lines connecting loops will remain. This is useful
       to remove all incorrect boundaries after other cleaning operations  with  thres  is  <  0.
       Areas can then be successfully built.

       To  preferentially  remove  shortest dangles first, a first pass with a small thresh value
       can be followed by subsequent passes with higher thresh values. This can be  done  as  one
       v.clean  job by listing the tool several times and by defining a list of increasing thresh

       The chdangle tool is similar to the rmdangle  tool,  but  works  only  on  boundaries  and
       changes dangling boundaries to lines instead of removing them.

   Remove or change bridges connecting an area and an island or two islands
       tool=rmbridge and tool=chbridge

       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  rmbridge
       tool removes bridges and the chbridge tool changes bridges to type line:
           +-------------+             +-------------+   +-------------+
           |            P|  P: polygon |            P|   |            P|
           |    +---+    |  I: island  |    +---+    |   |    +---+    |
           |    | I |    |  B: bridge  |    | I |    |   |    | I |    |
           |    |   |    |  L: line    |    |   |    |   |    |   |    |
           |    +-+-+    |             |    +---+    |   |    +-.-+    |
           |      |      |             |             |   |      .      |
           |      | B    |             |             |   |      . L    |
           |      |      |             |             |   |      .      |
           +------+------+             +-------------+   +-------------+

       Islands  and  areas  must  be  already  clean,  i.e. without dangles or small angles, e.g.
       v.clean ... type=boundary tool=rmdangle,rmsa,break,rmdupl,rmbridge thresh=-1,0,0,0,0.

       Threshold does not apply (it is ignored), use an arbitrary value (e.g., 0) if  v.clean  is
       run with several tools.

   Snap lines to vertex in threshold

       The  snap  tool snaps vertices to another vertex not farther away than thresh. If there is
       no other vertex within thresh, no snapping will be done. The type option can have a strong
       influence  on the result. A too large threshold and type=boundary can severely damage area
       topology, beyond repair.

       Threshold gives maximum distance to another vertex in map  units,  for  latitude-longitude
       locations in degree.

       Snapped boundaries may need to be cleaned with break,rmdupl,rmsa.

   Remove duplicate area centroids

       The rmdac tool removes duplicate area centroids that can result from deleting boundaries.

       Threshold  does  not apply (it is ignored), use an arbitrary value (e.g., 0) if v.clean is
       run with several tools.

   Break (topologically clean) areas (imported from a non topological
       format like ShapeFile) tool=bpol

       The bpol 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 bpol tool behaves similar to break  for  boundaries,  but  does  not  break
       collapsed loops. The bpol tool is faster than the break tool but needs more memory.

       Threshold  does  not apply (it is ignored), use an arbitrary value (e.g., 0) if v.clean is
       run with several tools.

       The bpol tool should be followed by rmdupl.

   Remove vertices in threshold from lines and boundaries

       The prune  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.   v.generalize  offers  much  more  functionality  for  line
       simplification but does not preserve area topology.

   Remove small areas

       The rmarea tool removes all areas <= thresh. 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.

       Threshold gives area size in map units, for latitude-longitude locations in square meters.

   Remove all lines or boundaries of zero length

       The rmline 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

       Threshold  does  not apply (it is ignored), use an arbitrary value (e.g., 0) if v.clean is
       run with several tools.

   Remove small angles between lines at nodes

       The rmsa tool only concerns angles which are so small that the calculated angle is 0.  The
       following figure should help demonstrate what the tool does.

       Threshold does not apply, use dummy value if v.clean is run with several tools.

            | tool=rmsa

       The  rmsa  tool should be followed by break,rmdupl. The rmsa tool followed by break,rmdupl
       may need to be run more than once to remove all small angles.


       The user does not have to run on the output vector, unless the -b flag  was  used.
       The -b flag affects only the output vector - topology is always built for error vector.


   Snap lines to vertex in threshold

       v.clean input=testmap output=cleanmap tool=snap thresh=1

   Cleaning OGR imported data (Simple Feature data) such as SHAPE file
       The import of areas with -c (no cleaning) requires a subsequent run of v.clean to
       update the map to a topologically valid structure (removal of  duplicate  collinear  lines
       etc). The tools used for that are bpol and rmdupl:
       v.clean input=areamap output=areamap_clean tool=bpol,rmdupl type=boundary

   Extracting intersection points of vector lines

       v.clean input=lines1 output=lines2 err=points tool=break type=line
        Intersection points are written to 'points' map.

   Break lines
       v.clean will break the lines where they cross, creating new node if needed. Example: -n out=crossed_lines format=standard << EOF
       L 2
        0 5
        10 5
       L 2
        5 0
        5 10
       v.clean in=crossed_lines out=crossed_lines_brk \
               error=intersection tool=break type=line

   Remove all lines of zero length

       v.out.ascii zero format=standard
       L  2 1
        -819832.09065589 -987825.2187231
        -806227.28362601 -971104.80702988
        1     1
       L  2 1
        -799165.24638913 -972974.16982788
        -799165.24638913 -972974.16982788
        1     2
       v.clean input=zero output=zero_clean tool=rmline type=line
       v.out.ascii zero_clean format=standard
       L  2 1
        -819832.09065589 -987825.2187231
        -806227.28362601 -971104.80702988
        1     1
        v.clean type=boundary would remove nothing.

   Repeatedly remove dangling lines up to 50m length

       v.clean input=testmap output=cleanmap type=line \
               tool=rmdangle,rmdangle,rmdangle,rmdangle thresh=5,10,20,50

SEE ALSO,, v.digit, v.edit


       David Gerdes, U.S. Army Construction Engineering Research Laboratory
       Radim Blazek, ITC-irst, Trento, Italy
       Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy

       Last changed: $Date: 2012-12-02 13:22:09 -0800 (Sun, 02 Dec 2012) $

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