GRASS GIS manual: v.to.db

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 layer=string [type=string[,string,...]] qlayer=string 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 vector map; Data source for direct OGR access
layer=string: Layer number or name (write to); A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.; Default: 1
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
qlayer=string: Query layer number or name (read from); A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.; 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; Options: miles,feet,meters,kilometers,acres,hectares,radians,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.addcolumn 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.addcolumn 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 D_L, 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.addcolumn 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

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: 2011-01-03 06:19:50 -0800 (Mon, 03 Jan 2011) $

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