## NAME

v.to.db - Load values from vector to database. In uploaded/printed category values '-1' is used for 'no category' and 'null'/'-' if category cannot be found or multiple categories were found.

## KEYWORDS

vector

## 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] [column=string[,string,...]] [qcolumn=string]

### Flags:

-p
  print only
-s
  only print sql statements
-c
  In print mode prints totals for options: length,area,count

### Parameters:

map=name
  Name of input vector map
type=string[,string,...]
  Type of elements (for coor valid point/centroid, for length valid line/boundary)
  Options: point,line,boundary,centroid
  Default: point,line,boundary,centroid
layer=integer
  Layer number
  Default: 1
qlayer=integer
  Query layer. Used by 'query' option.
  Default: 1
option=string
  Value to upload
  Options: cat,area,compact,perimeter,length,count,coor,start,end,sides,query
  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))
  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
units=string
  mi(les),f(eet),me(ters),k(ilometers),a(cres),h(ectares)
  Options: mi,miles,f,feet,me,meters,k,kilometers,a,acres,h,hectares
column=string[,string,...]
  column(s)
qcolumn=string
  Query 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.

## 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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