v.to.points(1grass) GRASS GIS User's Manual v.to.points(1grass)
NAME
v.to.points - Creates points along input lines in new vector map with
2 layers.
KEYWORDS
vector, geometry, 3D, line, node, vertex, point
SYNOPSIS
v.to.points
v.to.points --help
v.to.points [-iprt] input=name [layer=string]
[type=string[,string,...]] output=name [use=string] [dmax=float]
[--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-i
Interpolate points between line vertices (only for use=vertex)
-p
Use dmax as percentage of line length
-r
Start from the end node
-t
Do not create attribute table
--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
Line layer number or name
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
type=string[,string,...]
Input feature type
Options: point, line, boundary, centroid, area, face, kernel
Default: point,line,boundary,centroid,face
output=name [required]
Name for output vector map
use=string
Use line nodes (start/end) or vertices only
Options: node, start, end, vertex
dmax=float
Maximum distance between points in map units or percentage with -p
Default: 100
DESCRIPTION
v.to.points creates points along input 2D or 3D lines, boundaries and
faces. Point features including centroids and kernels are copied from
input vector map to the output. For details see notes about type param-
eter.
The output is a vector map with 2 layers. Layer 1 holds the category of
the input features; all points created along the same line have the
same category, equal to the category of that line. In layer 2 each
point has its unique category; other attributes stored in layer 2 are
lcat - the category of the input line and along - the distance from
line’s start.
By default only features with category are processed, see layer parame-
ter for details.
NOTES
The dmax parameter is the maximum limit but not an exact distance. To
place points with exact distance from the beginning of the vector line
the user should use v.segment.
Set layer to -1 to process features from all layers including features
without category. Features will be assigned new unique categories at
layer 1. Option layer=-1 should be used to convert boundaries, as in
most of cases boundaries lack category values.
The type parameter is used to control which input vector geometry types
to convert into points. Some caveats to consider about this parameter:
• Points and centroids can be considered as "lines" with only one
node. Consequently, the result of selecting point or centroid
as the type parameter is that all points/centroids get written
into the output vector map. The original category numbers of
the input points/centroids get written to the ’lcat’ attribute
in layer 2 of the output vector map. All values for along are
zero in the output vector map, as only point geometry was used
for input (there is no linear distance to calculate along, as
each point/centroid is the start and end of its own "line").
• Boundaries are treated as lines, with points getting interpo-
lated along the boundary perimeter according to dmax. If two
adjoining polygons share a topological boundary, the boundary
only gets converted to points once.
• If the type parameter is set to area, the boundary of each area
is converted to points regardless of whether or not there is a
topological boundary between adjacent areas. In other words,
the common boundary of two adjoining areas, for example, gets
converted to points twice. The centroid is not converted to a
point in the output vector for type=area.
The use=vertex option is used to digitize points that fall on the
line’s vertices only. Parameter dmax is ignored in this case. Similarly
to use=node when only line’s node are used. To filter only start-
ing/ending nodes use use=start/end.
If the -i flag is used in conjunction with the use=vertex option,
v.to.points will digitize points on the line vertices, as well as in-
terpolate points between line vertices using dmax as the maximum allow-
able spacing.
Use the -p flag to treat dmax as a percentage of each line length. For
example, to get points created for the beginning, middle and end only,
use the -p flag and set dmax so that:
50 < dmax <= 100
Hence, if dmax is between 0.5x and 1.0x the line length, you will al-
ways get points created at exactly the beginning, middle and end of the
input line.
Use the -r flag to create points starting from the end node.
EXAMPLES
Points along the input lines
In this example, the ’railroads’ vector lines map of the North Carolina
sample dataset is used to create points along the input lines:
# The North Carolina data are metric.
# 200m distance for points (maximum limit but not an exact distance)
v.to.points input=railroads output=railroads_points dmax=200
# verify the two layers in the resulting map
v.category input=railroads_points option=report
# vector info
v.info map=railroads_points
Extract nodes as points
v.to.points input=railroads output=railroads_nodes use=node
Extract starting/ending nodes as points
v.to.points input=railroads output=railroads_start use=start
v.to.points input=railroads output=railroads_end use=end
SEE ALSO
v.segment, v.split, v.to.rast, v.to.db
AUTHOR
Radim Blazek
Updated to GRASS 7 by Martin Landa, Czech Technical University in
Prague, Czech Republic
SOURCE CODE
Available at: v.to.points source code (history)
Accessed: unknown
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GRASS 7.8.7 v.to.points(1grass)
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