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v.to.db.1grass

NAME

v.to.db

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.

NOTES

The units miles, feet, meters and kilometers are square for option=area.

When using option=coor on a vector area map, only coordinates of centroids with unique category will be reported.

When calculating perimeters in Latitude-Longitude locations, the geodesic distance between the vertices is used.

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=area option=cat

Upload area sizes of each polygon to attribute table:

v.to.db map=soils type=area 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 of attributes from character column (with numeric contents) to 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/right polygons neighboring boundaries to attribute table:

# add boundary categories into geometry at layer 2:
v.category soils out=mysoils layer=2 type=boundary option=add
# add table with left/right column to layer 2:
v.db.addtable mysoils layer=2 col="left integer,right integer"
# upload categories of left/right polygons:
v.to.db mysoils option=sides col=left,right layer=2
# display the result:
v.db.select mysoils layer=2

Printing reports

Print x,y,z coordinates using dummy columns. The columns don't have to exist in the table for the features to be reported. Even a table is not required:
v.to.db -p bugsites option=coor type=point column=dummy1,dummy2
Report all area sizes of a map:

v.to.db -p soils option=area type=boundary units=h

Report all area sizes of a map, sorted by category number:

v.to.db -p soils option=area type=boundary units=h | sort -n

Report all line lengths of a map:

v.to.db -p roads option=length type=line units=k

Report number of features for each category in map:

v.to.db -p roads option=count type=line

SEE ALSO

v.category v.db.addtable v.db.addcol v.db.connect v.distance db.execute v.what d.what.vect

AUTHOR

Radim Blazek

Last changed: $Date: 2006/09/22 12:22:10 $

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