v.buffer(1grass) GRASS GIS User's Manual v.buffer(1grass)
NAME
v.buffer - Creates a buffer around vector features of given type.
KEYWORDS
vector, buffer, area, circle, geometry, line, grow, shrink
SYNOPSIS
v.buffer
v.buffer --help
v.buffer [-sct] input=name [layer=string] [cats=range]
[where=sql_query] [type=string[,string,...]] output=name [dis-
tance=float] [minordistance=float] [angle=float] [column=name]
[scale=float] [tolerance=float] [--overwrite] [--help] [--ver-
bose] [--quiet] [--ui]
Flags:
-s
Make outside corners straight
-c
Do not make caps at the ends of polylines
-t
Transfer categories and attributes
--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
cats=range
Category values
Example: 1,3,7-9,13
where=sql_query
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and population >= 10000
type=string[,string,...]
Input feature type
Options: point, line, boundary, centroid, area
Default: point,line,area
output=name [required]
Name for output vector map
distance=float
Buffer distance along major axis in map units
minordistance=float
Buffer distance along minor axis in map units
angle=float
Angle of major axis in degrees
Default: 0
column=name
Name of column to use for buffer distances
scale=float
Scaling factor for attribute column values
Default: 1.0
tolerance=float
Maximum distance between theoretical arc and polygon segments as
multiple of buffer (default 0.01)
DESCRIPTION
v.buffer creates a buffer around features of given type, which have a
category in the given layer. The tolerance controls the number of vec-
tor segments being generated (the smaller the value, the more vector
segments are generated).
NOTES
Internal buffers for areas can be generated with negative distance val-
ues ("inward buffer" or "negative buffer" or "shrinking").
v.buffer fusions the geometries of buffers by default. Categories and
attribute table will not be transferred (this would not make sense as
one buffer geometry can be the result of many different input geome-
tries). To transfer the categories and attributes the user can set the
t flag. This will result in buffers being cut up where buffers of indi-
vidual input geometries overlap. Each part that is the result of over-
lapping buffers of multiple geometries will have multiple categories
corresponding to those geometries, and multiple buffer areas can have
the same category. The buffer for the input feature with category X can
thus be retrieved by selecting all buffer areas with category X (see
example below).
Buffers for lines and areas are generated using the algorithms from the
GEOS library.
For advanced users: built-in buffer algorithm no longer desired, we use
GEOS: If GRASS is not compiled with GEOS support or environmental vari-
able GRASS_VECTOR_BUFFER is defined, then GRASS generates buffers using
built-in buffering algorithm (which is still buggy for some input
data).
The options minordistance, angle, tolerance are kept for backward com-
patibility and have no effect with GEOS buffering.
Corner settings
The following vector line related corners (also called "cap") exist:
• no cap:
• rounded cap:
• square cap:
By default v.buffer creates rounded buffers (blue color on figure be-
low): Straight corners with caps are created by -s flag (red color on
the figure below), while -c flag doesn’t make caps at the ends of poly-
lines (green color on the figure below): Using -s with a point vector
map as input data, square buffers are created instead of round buffers.
EXAMPLES
All examples are based on the North Carolina sample dataset.
Buffer around input lines
v.buffer input=roadsmajor output=roadsmajor_buffer type=line distance=100
Buffer of 100m along the "roadsmajor" lines (map subset, original cen-
ter line shown in black)
Circles around input points
v.buffer input=hospitals output=hospitals_circled type=point distance=2000
Buffer of 2000m around the "hospitals" points (map subset, original
points shown in black, new area centroids in red)
Circles around input points with attribute transfer
v.buffer input=hospitals output=hospitals_circled type=point distance=1000 -t
# display buffer around hospital with category 36,
# this buffer is composed of several areas:
d.vect map=hospitals_circled type=area layer=1 cats=36
# extract this buffer, dissolving boundaries
v.extract in=hospitals_circled output=hospital_36_circled layer=1 cats=36 -d
Buffer around input areas
v.buffer input=lakes output=lakes_buffer type=area distance=100
Buffer of 100m around the "lakes" polygons (map subset, original areas
shown in black)
Buffer inside input areas
In this example, an internal buffer ("inward buffer" or "negative buf-
fer") is generated using a negative distance value:
v.buffer input=lakes output=lakes_buffer type=area distance=-50
Internal buffer of 50m inside the "lakes" polygons (map subset, origi-
nal areas shown in black)
Not all features are buffered, only the polygons that allow creation
inside a topological cleaned polygon.
REFERENCES
• GEOS Library
SEE ALSO
r.buffer, v.parallel, v.extract, v.type, v.patch, v.db.connect
AUTHORS
Radim Blazek
Rewritten by Rosen Matev (with support through the Google Summer of
Code program 2008)
Rewritten by Markus Metz (2011, 2012)
SOURCE CODE
Available at: v.buffer source code (history)
Accessed: unknown
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GRASS 7.8.7 v.buffer(1grass)
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