NAME

KEYWORDS

SYNOPSIS

Flags:

-p

Print output to stdout, don't update attribute table. First column is always category of 'from' feature called from_cat

-a

Calculate distances to all features within the threshold. The output is written to stdout but may be uploaded to a new table created by this module. From categories are may be multiple

--overwrite

Force overwrite of output files

Parameters:

from=name

Name of existing vector file

to=name

Name of existing vector file

from_type=string[,string,...]

From type

Options: point,centroid

Default: point

to_type=string[,string,...]

To type

Options: point,line,boundary,centroid,area

Default: point,line,area

from_layer=integer

From layer

Default: 1

to_layer=integer

To layer

Default: 1

output=name

New vector map containing lines connecting nearest elements

dmax=float

Maximum distance or -1 for no limit

Default: -1

upload=string[,string,...]

Values describing the relation between two nearest features:
cat - category of the nearest feature
dist - minimum distance to nearest feature
to_x - x coordinate of the nearest point on 'to' feature
to_y - y coordinate of the nearest point on 'to' feature
to_along - distance to the nearest point on 'from' feature along linear feature
to_angle - angle of linear feature in nearest point, counterclockwise from positive x axis, in radians, which is between -PI and PI inclusive
to_attr - attribute of nearest feature given by to_column option

Options: cat,dist,to_x,to_y,to_along,to_angle,to_attr

column=string[,string,...]

Column name(s) where values specified by 'upload' option will be uploaded

to_column=string

Column name of nearest feature (used with upload=to_attr)

table=string

The name of the table created for output when -a flag is used

DESCRIPTION

EXAMPLES

v.distance from=pnt to=ln upload=cat column=linecat

2) For each point from vector map pnt find nearest area from map ar within the given threshold and write the related area categories to column areacat in attribute table attached to vector map pnt. In case a point falls into a polygon area, the distance is zero:

v.distance from=pnt to=ar upload=cat column=areacat

3) Create a new vector map which contains lines connecting nearest features of maps pnt and map ln. The resulting vector map can be used for example to connect points to a network as needed for network analysis:

v.distance -p from=pnt to=ln out=connections upload=dist column=dist

4) Query information from selected point(s). v.distance takes points from vector as input instead of stdin. First new vector map with query points, has to be created, then the map can be analysed:
Create query map (if not present):

echo "123456|654321|1" | v.in.ascii output=pnt

v.distance from=pnt to=map_to_query upload=cat col=somecol -p

5) Point-in-polygon: Find area from vector map ar for each point from vector map pnt in which the individual point falls into and write the related area categories to column areacat into attribute table attached to vector map pnt:

v.distance from=pnt to=ar dmax=0 upload=cat column=areacat

6) 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 bugs 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

# create working copy
g.copy vect=bugsites,bugs

# add new attribute column to hold nearest archsite category number
v.db.addcol map=bugs column="nrst_arch INTEGER"

v.distance from=bugs to=archsites to_type=point upload=to_attr \
  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 v=vdistance_vectors_raw

v.db.addtable map=vdistance_vectors column="length DOUBLE"
v.to.db map=vdistance_vectors option=length column=length

# calculcate statistics. Use v.univar.sh for extended statistics.
v.univar vdistance_vectors column=length

NOTES

The upload column(s) must already exist. Create one with v.db.addcol.

SEE ALSO

AUTHOR

5.0 cmd line coordinates support: Markus Neteler, ITC-irst, Trento, Italy

5.1 update Radim Blazek, ITC-irst, Trento, Italy

Last changed: $Date: 2006/03/30 11:40:14 $

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