Difference between revisions of "Vector remove small lines"

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(+v.clean approach)
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'''Q:''' How to remove small vector lines? I want to only delete spurious lines.
 
'''Q:''' How to remove small vector lines? I want to only delete spurious lines.
  
'''A1:''' You may the following approach:
+
'''A:''' You may choose from the following approach:
 +
 
 +
'''Approach 1:'''
 +
 
 +
Considering short vector segments as dangles, use:
 +
  {{cmd|v.clean}} in={your input vector} tool=rmdangle thresh={your threshold} out={output vector}
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 +
'''Approach 2:'''
  
 
* use {{cmd|v.build.polylines}} to join broken vector segments into longer segments
 
* use {{cmd|v.build.polylines}} to join broken vector segments into longer segments
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   {{cmd|v.extract}} in=mypolyline out=mypolyline_over5km type=line where="length_km > 5.0"
 
   {{cmd|v.extract}} in=mypolyline out=mypolyline_over5km type=line where="length_km > 5.0"
  
'''A2:''' Alternative approach:
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'''Approach 3:'''
  
Removes from vector map all lines with length shorter than 50 map units (thresh: threshold distance (coords,snap,query)):
+
Remove from vector map all lines with length shorter than 50 map units (thresh: threshold distance (coords,snap,query)):
 
  {{cmd|v.edit}} mymap tool=delete query=length thresh=-1,0,-50 type=line
 
  {{cmd|v.edit}} mymap tool=delete query=length thresh=-1,0,-50 type=line
  

Revision as of 07:49, 4 November 2014

Q: How to remove small vector lines? I want to only delete spurious lines.

A: You may choose from the following approach:

Approach 1:

Considering short vector segments as dangles, use:

  v.clean in={your input vector} tool=rmdangle thresh={your threshold} out={output vector}

Approach 2:

  • use v.build.polylines to join broken vector segments into longer segments
  • then use v.to.db with option=length (line length) to upload the vector segment lengths to the attribute table
  v.db.addcol mypolyline column="length_km double precision"
  v.to.db mypolyline type=line option=length units=k column=length_km
  • now use v.extract to extract the longer vector segments into a new map according to a threshold you need. Example: Extract line features longer than 5km (cleans out the noise):
  v.extract in=mypolyline out=mypolyline_over5km type=line where="length_km > 5.0"

Approach 3:

Remove from vector map all lines with length shorter than 50 map units (thresh: threshold distance (coords,snap,query)):

v.edit mymap tool=delete query=length thresh=-1,0,-50 type=line

See also