.TH v.distance 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.distance\fR\fR  \- Finds the nearest element in vector map \(cqto\(cq for elements in vector map \(cqfrom\(cq.
.SH KEYWORDS
vector, distance, database, attribute table
.SH SYNOPSIS
\fBv.distance\fR
.br
\fBv.distance \-\-help\fR
.br
\fBv.distance\fR [\-\fBpa\fR] \fBfrom\fR=\fIname\fR  [\fBfrom_layer\fR=\fIstring\fR]   [\fBfrom_type\fR=\fIstring\fR[,\fIstring\fR,...]]  \fBto\fR=\fIname\fR  [\fBto_layer\fR=\fIstring\fR]   [\fBto_type\fR=\fIstring\fR[,\fIstring\fR,...]]   [\fBoutput\fR=\fIname\fR]   [\fBdmax\fR=\fIfloat\fR]   [\fBdmin\fR=\fIfloat\fR]   [\fBupload\fR=\fIstring\fR[,\fIstring\fR,...]]   [\fBcolumn\fR=\fIname\fR[,\fIname\fR,...]]   [\fBto_column\fR=\fIname\fR]   [\fBtable\fR=\fIname\fR]   [\fBseparator\fR=\fIcharacter\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-p\fR" 4m
.br
Print output to stdout, don\(cqt update attribute table
.br
First column is always category of \(cqfrom\(cq feature called from_cat
.IP "\fB\-a\fR" 4m
.br
Calculate distances to all features within the threshold
.br
Output may be written to stdout using the \(cq\-p\(cq flag or uploaded to a new table created by the \(cqtable\(cq option; multiple \(cqupload\(cq options may be used.
.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 "\fBfrom\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of existing vector map (from)
.br
Or data source for direct OGR access
.IP "\fBfrom_layer\fR=\fIstring\fR" 4m
.br
Layer number or name (from)
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI1\fR
.IP "\fBfrom_type\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Feature type (from)
.br
Input feature type
.br
Options: \fIpoint, line, boundary, centroid, area\fR
.br
Default: \fIpoint,line,area\fR
.IP "\fBto\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of existing vector map (to)
.br
Or data source for direct OGR access
.IP "\fBto_layer\fR=\fIstring\fR" 4m
.br
Layer number or name (to)
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI1\fR
.IP "\fBto_type\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Feature type (to)
.br
Input feature type
.br
Options: \fIpoint, line, boundary, centroid, area\fR
.br
Default: \fIpoint,line,area\fR
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output vector map containing lines connecting nearest elements
.IP "\fBdmax\fR=\fIfloat\fR" 4m
.br
Maximum distance or \-1 for no limit
.br
Map units, meters for ll
.br
Default: \fI\-1\fR
.IP "\fBdmin\fR=\fIfloat\fR" 4m
.br
Minimum distance or \-1 for no limit
.br
Map units, meters for ll
.br
Default: \fI\-1\fR
.IP "\fBupload\fR=\fIstring[,\fIstring\fR,...]\fR" 4m
.br
Values describing the relation between two nearest features
.br
Options: \fIcat, dist, to_x, to_y, to_along, to_angle, to_attr\fR
.br
\fBcat\fR: category of the nearest feature
.br
\fBdist\fR: minimum distance to nearest feature
.br
\fBto_x\fR: x coordinate of the nearest point on the \(cqto\(cq feature
.br
\fBto_y\fR: y coordinate of the nearest point on the \(cqto\(cq feature
.br
\fBto_along\fR: distance to the nearest point on the \(cqto\(cq feature along that linear feature
.br
\fBto_angle\fR: angle along the nearest linear feature in the \(cqto\(cq map, measured CCW from the +x axis, in radians, between \-Pi and Pi inclusive
.br
\fBto_attr\fR: attribute of nearest feature given by to_column option
.IP "\fBcolumn\fR=\fIname[,\fIname\fR,...]\fR" 4m
.br
Column name(s) where values specified by \(cqupload\(cq option will be uploaded
.IP "\fBto_column\fR=\fIname\fR" 4m
.br
Column name of nearest feature (used with upload=to_attr)
.IP "\fBtable\fR=\fIname\fR" 4m
.br
Name for new attribute table
.IP "\fBseparator\fR=\fIcharacter\fR" 4m
.br
Field separator for printing output to stdout
.br
Special characters: pipe, comma, space, tab, newline
.br
Default: \fIpipe\fR
.SH DESCRIPTION
\fIv.distance\fR finds the nearest element in vector map (\fBto\fR)
for elements in vector map (\fBfrom\fR). Various information about
the vectors\(cq relationships (distance, category, etc.) may be uploaded to
the attribute table attached to the first vector map, or printed to
\(cqstdout\(cq. A new vector map may be created where lines connecting
nearest points on features are written. \fBdmin\fR and/or
\fBdmax\fR can be used to limit the search radius (in lat\-long locations
to be given in meters since they are calculated as geodesic distances on
a sphere).
.PP
For lines to lines, say line A to line B, \fIv.distance\fR calculates
the shortest distance of each vertex in A with each segment (not vertex)
in B. The module then calculates the shortest distance of each vertex in
B to each segment in A. The overall shortest distance of A points to B
segments and B points to A segments is used. Additionally,
\fIv.distance\fR checks for intersections. In case of intersections,
the first intersection found is used and the distance set to zero.
.PP
For lines to areas, the distance is set to zero if a line is (partially)
inside an area. The first point of the line that is inside the area is
used as common point. The distance is also set to zero if the line
intersects with the outer ring or any of the inner rings (isles), in
which case the fist intersection is used as common point.
.PP
For areas to areas, the module checks first for overlap or if one area
is (partially) inside the other area. This is computationally quite
intensive. If the outer rings of the two areas do not overlap, the
distance is calculated as above for lines to lines, treating the outer
rings as two lines. Again, the first point encountered falling into an
area is used as common point, or the first intersection point.
.PP
For anything else than points to lines, there can be several common
locations with zero distance, and the common location would then be the
result of an overlay consisting of several points, lines, or areas.
\fIv.distance\fR selects in these cases a single point, and does
not create an overlay
like \fIv.overlay\fR. In this
implementation, any shared point is as good as any other. Calculating
an intersection is costlier than to check if a vertex is inside a
polygon. For example, if a vertex of the boundary of the \(cqto\(cq area is
inside the \(cqfrom\(cq area, it is a common location. For speed reasons,
the distance is then set to zero and no further tests are done.
.SH NOTES
If a nearest feature does not have a category, the attribute column is
updated to NULL.
.PP
The upload \fBcolumn\fR(s) must already exist. Create one with
\fIv.db.addcolumn\fR.
.PP
In lat\-long locations \fIv.distance\fR gives distances
(\fIdist\fR, \fIfrom_along\fR, and \fIto_along\fR) not in
degrees but in meters calculated as geodesic distances on a sphere.
.PP
If one or both of the input vector maps are 3D, the user is notified
accordingly.
.SH EXAMPLES
.SS Find nearest lines
Find \fInearest lines\fR in vector map \(dqln\(dq for points from
vector map \(dqpnt\(dq within the given threshold and write related
line categories to column \(dqlinecat\(dq in an attribute table attached
to vector map \(dqpnt\(dq:
.br
.nf
\fC
v.distance from=pnt to=ln upload=cat column=linecat
\fR
.fi
.SS Find nearest area
For each point from vector map \(dqpnt\(dq, find the \fInearest area\fR
from map \(dqar\(dq within the given threshold and write the related
area categories to column \(dqareacat\(dq in an attribute table attached
to vector map \(dqpnt\(dq (in the case that a point falls into an area,
the distance is zero):
.br
.nf
\fC
v.distance from=pnt to=ar upload=cat column=areacat
\fR
.fi
.SS Create a new vector map
Create a new vector map which contains \fIlines connecting nearest
features\fR of maps \(dqpnt\(dq and map \(dqln\(dq. The resulting
vector map can be used for example to connect points to a network as
needed for network analysis:
.br
.nf
\fC
v.distance from=pnt to=ln out=connections upload=dist column=dist
\fR
.fi
.SS Create a new vector map with from and to categories in the attribute table
Create a new vector map that contains \fIlines connecting nearest
features\fR of maps \(dqpnt\(dq and map \(dqln\(dq, and a new
attribute table that contains distances, from and to categories from the
input maps:
.br
.nf
\fC
v.distance from=pnt to=ln out=connections upload=cat,dist column=to_cat,dist table=connections
\fR
.fi
.SS Query information
Query information from selected point(s). \fIv.distance\fR takes
points from a vector map as input instead of stdin. A new vector map
with query points has to be created before the map can be analysed.
.PP
Create query map (if not present):
.br
.nf
\fC
echo \(dq123456|654321|1\(dq | v.in.ascii output=pnt
\fR
.fi
Find nearest features:
.br
.nf
\fC
v.distance \-p from=pnt to=map_to_query upload=cat
\fR
.fi
.SS Point\-in\-polygon
The option \fBdmax=0\fR is here important because otherwise for
points not falling into any area, the category of the nearest area is
recorded.
.br
For each point from vector map \(dqpnt\(dq, find the \fIarea\fR from
vector map \(dqar\(dq in which the individual point falls, and
write the related area categories to column \(dqareacat\(dq into
the attribute table attached to vector map \(dqpnt\(dq:
.br
.nf
\fC
v.distance from=pnt to=ar dmax=0 upload=cat column=areacat
\fR
.fi
.SS Univariate statistics on results
Create a vector map containing connecting lines and investigate mean
distance to targets. An alternative solution is to use
the v.distance upload=dist option to upload distances into
the \fIbugs\fR vector directly, then run v.univar on that. Also note
you can upload two columns at a time, e.g. v.distance
upload=cat,dist column=nearest_id,dist_to_nr.
.br
.nf
\fC
# create working copy
g.copy vect=bugsites,bugs
# add new attribute column to hold nearest archsite category number
v.db.addcolumn map=bugs column=\(dqnrst_arch INTEGER\(dq
v.distance from=bugs to=archsites to_type=point upload=to_attr \(rs
  to_column=cat column=nrst_arch out=vdistance_vectors_raw
# we need to give the lines category numbers, create a table, and create
#  a column in that table to hold the distance data.
v.category vdistance_vectors_raw out=vdistance_vectors type=line op=add
g.remove \-f type=vector name=vdistance_vectors_raw
v.db.addtable map=vdistance_vectors column=\(dqlength DOUBLE\(dq
v.to.db map=vdistance_vectors option=length column=length
# calculate statistics
v.univar vdistance_vectors column=length
\fR
.fi
.SS Print distance between points
Example for a Latitude\-longitude location (EPSG 4326):
.br
.nf
\fC
# points along the equator
echo \(dq0|\-61|1\(dq | v.in.ascii output=pnt1 input=\-
echo \(dq0|\-58|1\(dq | v.in.ascii output=pnt2 input=\-
# here, distances are in degree units
v.distance \-p \-\-q from=pnt1 to=pnt2 upload=dist
from_cat|distance
1|3
\fR
.fi
.SS Print distance matrix
Note: Matrix\-style output is enabled only for flag \fI\-a\fR and one
given upload option.
.PP
Spearfish sample data location:
.br
.nf
\fC
v.distance \-pa from=archsites to=archsites upload=dist
\fR
.fi
.PP
North Carolina sample data location:
.br
.nf
\fC
v.distance \-pa from=hospitals to=hospitals upload=dist separator=tab
from_cat to_cat       dist
              1          2          3          4          5 ...
1             0    7489.10  339112.17   70900.39   70406.23 ...
2       7489.10          0  345749.12   76025.46   75538.87 ...
3     339112.17  345749.12          0  274153.19  274558.98 ...
4      70900.39   76025.46  274153.19          0     501.11 ...
5      70406.23   75538.87  274558.98     501.11          0 ...
\&...
\fR
.fi
.SH SEE ALSO
\fI
r.distance,
v.db.addcolumn,
v.what.vect
\fR
.SH AUTHORS
Janne Soimasuo 1994, University of Joensuu, Faculty of Forestry, Finland
.br
Cmd line coordinates support: Markus Neteler, ITC\-irst, Trento, Italy
.br
Updated for 5.1: Radim Blazek, ITC\-irst, Trento, Italy
.br
Matrix\-like output by Martin Landa, FBK\-irst, Trento, Italy
.br
Improved processing speed: Markus Metz
.br
Distance from any feature to any feature: Markus Metz
.br
New table without the \-p flag: Huidae Cho
.SH SOURCE CODE
.PP
Available at: v.distance source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual