## NAME

v.patch - Creates a new binary vector map layer by combining other binary vector map layers.
(GRASS Vector Program)

## SYNOPSIS

v.patch
v.patch help
v.patch input=name[,name,...] output=name

## DESCRIPTION

v.patch allows the user to combine any number of vector map layers together to create one composite vector map layer.

## OPTIONS

### Parameters:

input=name,name, ...
  Name(s) of input vector map(s) to be patched together.
output=name
  Name assigned to composite "patched" vector output map.

The program will be run non-interactively if the user specifies the names of the vector map(s) to be patched and the name of an output file to store the resulting composite patched vector map on the command line, in the form:

  v.patch input=name[,name,...] output=name

Alternately, if the user runs v.patch without specifying input and output file names on the command line (by typing simply v.patch), the program will prompt the user for inputs using the standard GRASS interface described in the manual entry for parser.

## NOTES

The vector map layers to be patched together must exist in the user's current mapset search path, and the composite vector map layer name given must not already exist in the user's current mapset.

After running v.patch, the header file will contain only information taken from the first input file name given in the string input=name,name, ..., with the exception of the geographic region's edge information, and the scale and threshold information. (The user's current geographic region settings are ignored; this information is instead extracted from the vector file headers.) In the new composite vector map layer, the boundaries of the geographic region will be expanded to encompass all of the geographic area included in the map layers being patched, and the scale will be set equal to the smallest (i.e., most gross) scale used by any of the patched map layers (this will affect default node-snapping thresholds). The map threshold is calculated automatically from the map scales given in the file headers, and (currently) is not used directly. The composite vector map layer's header will probably need to be edited; this can be done from within the GRASS program v.digit.

The GRASS programs v.mkgrid and v.mkquads can be used to ensure that the borders of the maps to be patched together align neatly.

Any vectors that are duplicated among the maps being patched together (e.g., border lines) will have to be edited or removed after v.patch is run. Such editing can be done using v.digit.

After running v.patch the user must run v.support on the composite vector map layer in order to create a `dig_plus` (topology) file for it. At this time, you can request that a very small snapping threshold be used, to cause the nodes that match up across vector map layers to snap together without affecting the integrity of the remainder of the vector map layer.

## BUGS

The `dig_cats` and `reg` file information for the maps being patched together is not copied to the composite, patched map layer. The user should therefore run v.support on the output file produced by this program.

## SEE ALSO

v.digit, v.in.ascii, v.mkgrid, v.mkquads, v.support, and parser

## AUTHOR

Dave Gerdes, U.S.Army Construction Engineering Research Laboratory

Last changed: $Date: 2002/01/25 05:45:35 $