.TH v.split 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.split\fR\fR  \- Splits vector lines to shorter segments.
.SH KEYWORDS
vector, geometry, densification, node, segment, vertex
.SH SYNOPSIS
\fBv.split\fR
.br
\fBv.split \-\-help\fR
.br
\fBv.split\fR [\-\fBnf\fR] \fBinput\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]  \fBoutput\fR=\fIname\fR  [\fBlength\fR=\fIfloat\fR]   [\fBunits\fR=\fIstring\fR]   [\fBvertices\fR=\fIinteger\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-n\fR" 4m
.br
Add new vertices, but do not split
.br
Applies only to \(cqlength\(cq option
.IP "\fB\-f\fR" 4m
.br
Force segments to be exactly of given length, except for last one
.br
Applies only to \(cqlength\(cq option
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector map
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name (\(cq\-1\(cq for all layers)
.br
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.
.br
Default: \fI\-1\fR
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output vector map
.IP "\fBlength\fR=\fIfloat\fR" 4m
.br
Maximum segment length
.IP "\fBunits\fR=\fIstring\fR" 4m
.br
Length units
.br
Options: \fImap, meters, kilometers, feet, surveyfeet, miles, nautmiles\fR
.br
Default: \fImap\fR
.IP "\fBvertices\fR=\fIinteger\fR" 4m
.br
Maximum number of vertices in segment
.SH DESCRIPTION
\fIv.split\fR splits vector lines into shorter segments using
a maximal distance between nodes. The resulting length of all segments
is expected to be equal and not higher than the given \fBlength\fR
parameter.
.SH NOTES
\fIv.split\fR 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 features with
their category as key, all segments originating from the same original
line are linked to the same line in the original attribute table which
is just copied to the new map.
.SS Notes on individual segment information
When running \fIv.to.db\fR on a map produced by \fIv.split\fR,
\fIv.to.db\fR 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 attribute table line, it only gets
updated once.
.PP
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 \fIv.category\fR
.br
.nf
\fC
v.category v_split op=add layer=2 output=v_split_2
\fR
.fi
and then run the following commands on the new layer 2:
.br
.nf
\fC
v.db.addtable v_split_2 layer=2
v.db.addcolumn map=v_split_2 column=\(dqlength double precision\(dq layer=2
v.to.db map=v_split_2 type=line option=length columns=length units=meters layer=2
\fR
.fi
To link the new segments in the new layer to the original segments, use:
.br
.nf
\fC
v.db.addcolumn map=v_split_2 layer=2 column=\(dqcat_1 int\(dq
v.to.db map=v_split_2 layer=2 option=query query_layer=1 query_column=cat columns=cat_1
\fR
.fi
.SH EXAMPLES
The examples are based on the North Carolina sample data location.
.SS Example 1: Inserting nodes to railroad lines map
.br
.nf
\fC
# 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
\fR
.fi
.PP
Note: In case that the vector line data are not polylines,
generate first polylines as the second step, eg.:
.br
.nf
\fC
# join segments into polyline
v.build.polylines input=myrr output=myrr_polylines
# regenerate categories
v.category input=myrr_polylines output=myrailroads option=add
\fR
.fi
.SS Example 2: Inserting vertices to railroad lines map
Note: first run the two steps from example 1.
.br
.nf
\fC
# 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
\fR
.fi
.SH SEE ALSO
\fI
v.edit,
v.build.polylines,
v.to.points,
v.segment
\fR
.SH AUTHOR
Radim Blazek
.SH SOURCE CODE
.PP
Available at: v.split source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual