v.clean

## NAME

v.clean - Toolset to clean vector topology

## KEYWORDS

vector

## SYNOPSIS

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

### Flags:

-b
  Do not rebuild and store the topology at the end
--overwrite
  Force overwrite of output files

### Parameters:

input=name
  Name of input vector map
output=name
  Name for output vector map
type=string[,string,...]
  Type
  Options: point,line,boundary,centroid,area
  Default: point,line,boundary,centroid,area
error=name
  Name of output map where errors are written
tool=string[,string,...]
  Cleaning tool
  Options: break,rmdupl,rmdangle,chdangle,rmbridge,chbridge,snap,rmdac,bpol,prune,rmarea,rmsa
  break: break lines at each intersection
  rmdupl: remove duplicate lines (pay attention to categories!)
  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
  snap: snap lines to vertex in threshold
  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 attachement of centroid), first and last segment of the boundary is never changed
  rmarea: remove small areas, the longest boundary with adjacent area is removed
  rmsa: remove small angles between lines at nodes
thresh=float[,float,...]
  Threshold
  Threshold in map units, one value for each tool (default: 0.0[,0.0,...])

## DESCRIPTION

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

## NOTES

The user does not have to run v.build 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.

### Removing small angles between lines at nodes

The rmsa tool only concerns angles which are so small that the calculated angle is 0. The user cannot change this threshold. The following figure should help to understand what the tool does.

### What is a bridge?

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). v.clean can be used to optionally change the line type to fulfill the topology rules or to remove the bridge from the map:

        +-------------+             +-------------+   +-------------+
        |            P|  P: polygon |            P|   |            P|
        |    +---+    |  I: island  |    +---+    |   |    +---+    |
        |    | I |    |  B: bridge  |    | I |    |   |    | I |    |
        |    |   |    |  L: line    |    |   |    |   |    |   |    |
        |    +-+-+    |             |    +---+    |   |    +-.-+    |
        |      |      |             |             |   |      .      |
        |      | B    |             |             |   |      . L    |
        |      |      |             |             |   |      .      |
        +------+------+             +-------------+   +-------------+

## EXAMPLES

### Snap lines to vertex in threshold

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

### Cleaning OGR imported data (Simple Feature data)

The import of areas with v.in.ogr 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 'rmdupl' and 'bpol':

    v.clean input=areamap output=areamap_clean tool=rmdupl,bpol

### Extracting intersection points of vector lines

    v.clean input=lines1 output=lines2 err=points tool=break

Intersection points are written to 'points' map.

### Break lines

v.clean will break the lines where they cross, creating new node if needed. Example:

    v.in.ascii -n out=crossed_lines format=standard << EOF
    L 2
     0 5
     10 5
    L 2
     5 0
     5 10
    EOF

    v.clean in=crossed_lines out=crossed_lines_brk \
            error=intersection tool=break

## AUTHORS

David Gerdes, U.S. Army Construction Engineering Research Laboratory
Radim Blazek, ITC-Irst, Trento, Italy

Last changed: $Date: 2006/09/29 21:22:55 $

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