v.split(1grass) GRASS GIS User's Manual v.split(1grass)
NAME
v.split - Splits vector lines to shorter segments.
KEYWORDS
vector, geometry, densification, node, segment, vertex
SYNOPSIS
v.split
v.split --help
v.split [-nf] input=name [layer=string] output=name [length=float]
[units=string] [vertices=integer] [--overwrite] [--help] [--ver-
bose] [--quiet] [--ui]
Flags:
-n
Add new vertices, but do not split
Applies only to ’length’ option
-f
Force segments to be exactly of given length, except for last one
Applies only to ’length’ option
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input vector map
Or data source for direct OGR access
layer=string
Layer number or name (’-1’ for all layers)
A single vector map can be connected to multiple database tables.
This number determines which table to use. When used with direct
OGR access this is the layer name.
Default: -1
output=name [required]
Name for output vector map
length=float
Maximum segment length
units=string
Length units
Options: map, meters, kilometers, feet, surveyfeet, miles, naut-
miles
Default: map
vertices=integer
Maximum number of vertices in segment
DESCRIPTION
v.split splits vector lines into shorter segments using a maximal dis-
tance between nodes. The resulting length of all segments is expected
to be equal and not higher than the given length parameter.
NOTES
v.split does not change the layer, nor the category information, nor
the attribute table links of the original file. It just splits each
line in segments and attributes the same category to all segments of
the same original line. As the attribute table is linked to the fea-
tures with their category as key, all segments originating from the
same original line are linked to the same line in the original attri-
bute table which is just copied to the new map.
Notes on individual segment information
When running v.to.db on a map produced by v.split, v.to.db will add
length information for each segment in its respective attribute line,
but since all the segments of the same original line share the same at-
tribute table line, it only gets updated once.
To obtain the length of each segment, the user will have to attribute
different category values to each of them. The best way to do this on a
separate layer, using v.category
v.category v_split op=add layer=2 output=v_split_2
and then run the following commands on the new layer 2:
v.db.addtable v_split_2 layer=2
v.db.addcolumn map=v_split_2 column="length double precision" layer=2
v.to.db map=v_split_2 type=line option=length columns=length units=meters layer=2
To link the new segments in the new layer to the original segments,
use:
v.db.addcolumn map=v_split_2 layer=2 column="cat_1 int"
v.to.db map=v_split_2 layer=2 option=query query_layer=1 query_column=cat columns=cat_1
EXAMPLES
The examples are based on the North Carolina sample data location.
Example 1: Inserting nodes to railroad lines map
# extract one railroad line for this example
v.extract input=railroads output=myrr cats=1
# show line, category, direction (to find the beginning)
g.region vector=myrr
d.erase
d.vect myrr display=shape,cat,dir
# insert nodes at a distance not longer than 1000m
v.split input=myrr output=myrr_split_1km length=1000
d.vect myrr_split_1km display=shape,topo
Note: In case that the vector line data are not polylines, generate
first polylines as the second step, eg.:
# join segments into polyline
v.build.polylines input=myrr output=myrr_polylines
# regenerate categories
v.category input=myrr_polylines output=myrailroads option=add
Example 2: Inserting vertices to railroad lines map
Note: first run the two steps from example 1.
# insert vertices at a distance not longer than 1000m
v.split -n input=myrr output=myrr_split length=1000
d.vect myrr_split display=shape,topo
SEE ALSO
v.edit, v.build.polylines, v.to.points, v.segment
AUTHOR
Radim Blazek
SOURCE CODE
Available at: v.split source code (history)
Accessed: unknown
Main index | Vector index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 v.split(1grass)
Generated by dwww version 1.14 on Sun Dec 29 19:29:08 CET 2024.