Provided by: grass-doc_6.4.3-3_all 
NAME
v.to.db - Populates database values from vector features.
KEYWORDS
vector, database, attribute table
SYNOPSIS
v.to.db
v.to.db help
v.to.db [-psc] map=name [type=string[,string,...]] [layer=integer] [qlayer=integer]
option=string [units=string] [columns=name[,name,...]] [qcolumn=name] [--verbose]
[--quiet]
Flags:
-p
Print only
-s
Only print SQL statements
-c
In print mode prints totals for options: length,area,count
--verbose
Verbose module output
--quiet
Quiet module output
Parameters:
map=name
Name of input vector map
type=string[,string,...]
Feature type
For coor valid point/centroid, for length valid line/boundary
Options: point,line,boundary,centroid
Default: point,line,boundary,centroid
layer=integer
Layer number (write to)
A single vector map can be connected to multiple database tables. This number
determines which table to use.
Default: 1
qlayer=integer
Query layer number (read from)
A single vector map can be connected to multiple database tables. This number
determines which table to use.
Default: 1
option=string
Value to upload
Options:
cat,area,compact,fd,perimeter,length,count,coor,start,end,sides,query,slope,sinuous,azimuth
cat: insert new row for each category if doesn't exist yet
area: area size
compact: compactness of an area, calculated as compactness = perimeter / (2 * sqrt(PI
* area))
fd: fractal dimension of boundary defining a polygon, calculated as fd = 2 *
(log(perimeter) / log(area))
perimeter: perimeter length of an area
length: line length
count: number of features for each category
coor: point coordinates, X,Y or X,Y,Z
start: line/boundary starting point coordinates, X,Y or X,Y,Z
end: line/boundary end point coordinates, X,Y or X,Y,Z
sides: categories of areas on the left and right side of the boundary, 'qlayer' is
used for area category
query: result of a database query for all records of the geometry(or geometries) from
table specified by 'qlayer' option
slope: slope steepness of vector line or boundary
sinuous: line sinuousity, calculated as line length / distance between end points
azimuth: line azimuth, calculated as angle between North direction and endnode
direction at startnode
units=string
Units
mi(les),f(eet),me(ters),k(ilometers),a(cres),h(ectares),r(adians),d(egrees)
Options: mi,miles,f,feet,me,meters,k,kilometers,a,acres,h,hectares,r,radians,d,degrees
columns=name[,name,...]
Name of attribute column(s)
qcolumn=name
Name of attribute column used for 'query' option
E.g. 'cat', 'count(*)', 'sum(val)'
DESCRIPTION
v.to.db loads vector map features or metrics into a database table, or prints them (or the
SQL queries used to obtain them) in a form of a human-readable report. For
uploaded/printed category values ’-1' is used for 'no category' and 'null'/'-' if category
cannot be found or multiple categories were found. For line azimuths '-1' is used for
closed lines (start equals end).
NOTES
The units miles, feet, meters and kilometers are square for option=area.
Feet and acre units are always reported in their common versions (i.e. the International
Foot, exactly 5280 feet in a mile), even when the location's standard map unit is the US
Survey foot.
When calculating perimeters in Latitude-Longitude locations, the geodesic distance between
the vertices is used.
When using option=coor on a vector area map, only coordinates of centroids with unique
category will be reported.
Line azimuth is calculated as angle from the North direction to the line endnode direction
at the line statnode. By default it's reported in decimal degrees (0-360, CW) but it also
may be repored in radians with unit=radians. Azimuth value -1 is used to report closed
line with it's startnode and endnode being in same place. Azimuth values make sense only
if every vector line has only one entry in database (unique CAT value).
If the module is apparently slow and the map attributes are stored in an external DBMS
such as PostgreSQL, it is highly recommended to create an index on the key (category)
column.
Uploading the vector map attributes to a database requires a table attached to a given
input vector layer. The print only (-p) mode doesn't require a table. Use db.execute or
v.db.addtable to create a table if needed.
Updating the table has to be done column-wise. The column must be present in the table,
except when using the print only (-p) mode. Use db.execute or v.db.addcol to add new
columns if needed.
EXAMPLES
Updating attribute tables
Upload category numbers to attribute table (used for new map):
v.to.db map=soils type=centroid option=cat
Upload polygon areas to corresponding centroid record in the attribute table:
v.to.db map=soils type=centroid option=area col=area_size unit=h
Upload line lengths (in meters) of each vector line to attribute table (use v.category in
case of missing categories):
v.to.db map=roads option=length type=line col=linelength units=me
Upload x and y coordinates from vector geometry to attribute table:
v.to.db map=pointsmap option=coor col=x,y
Upload x, y and z coordinates from vector geometry to attribute table:
v.to.db map=pointsmap option=coor col=x,y,z
Transfer attributes from a character column (with numeric contents) to a new integer
column:
v.db.addcol usa_income_employment2002 col="FIPS_NUM integer"
v.to.db usa_income_employment2002 option=query col=FIPS_NUM qcol=STATE_FIPS
Upload category numbers of left and right area, to an attribute table of boundaries common
for the areas:
# add categories for boundaries of the input vector map, in layer 2:
v.category soils out=mysoils layer=2 type=boundary option=add
# add a table with columns named "left" and "right" to layer 2 of the input
# vector map:
v.db.addtable mysoils layer=2 col="left integer,right integer"
# upload categories of left and right areas:
v.to.db mysoils option=sides col=left,right layer=2
# display the result:
v.db.select mysoils layer=2
Compute DL, the Fractal Dimension (Mandelbrot, 1982), of the boundary defining a polygon
based on the formula:
D = 2 * (log perimeter) / (log area):
g.copy vect=soils,mysoils
v.db.addcol mysoils col="d double precision"
v.to.db mysoils option=fd column="d"
g.region vect=mysoils res=50
v.to.rast in=mysoils out=soils_fd type=area use=attr column=d
r.colors map=soils_fd color=gyr
d.mon x0
d.rast.leg soils_fd
d.vect mysoils type=boundary
Printing reports
Report x,y,z coordinates of points in the input vector map:
v.to.db -p bugsites option=coor type=point
Report all area sizes of the input vector map:
v.to.db -p soils option=area type=boundary units=h
Report all area sizes of the input vector map, in hectares, sorted by category number
(requires GNU sort utility installed):
v.to.db -p soils option=area type=boundary units=h | sort -n
Report all line lengths of the input vector map, in kilometers:
v.to.db -p roads option=length type=line units=k
Report number of features for each category in the input vector map:
v.to.db -p roads option=count type=line
SEE ALSO
d.what.vect, db.execute, v.category, v.db.addtable, v.db.addcol, v.db.connect,
v.distance, v.report, v.univar, v.what
REFERENCES
Mandelbrot, B. B. (1982). The fractal geometry of nature. New York: W. H. Freeman. Xu, Y.
F. & Sun, D. A. (2005). Geotechnique 55, No. 9, 691-695
AUTHOR
Radim Blazek, ITC-irst, Trento, Italy
Line sinuousity implemented by Wolf Bergenheim
Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $
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