r.buffer <main>	      GRASS Reference Manual	  <main> r.buffer



NAME
     r.buffer - Creates a raster map layer showing buffer zones
     surrounding cells that contain non-zero category values.
     (GRASS Raster Program)

SYNOPSIS
     r.buffer
     r.buffer help
     r.buffer [-q] input=name output=name
	distances=value[,value,...]  [units=name]

DESCRIPTION
     r.buffer creates a new raster map layer showing buffer
     (a.k.a. "distance" or "proximity") zones around all cells
     that contain non-zero category values in an existing raster
     map layer.	 The distances of buffer zones from cells with
     non-zero category values are user-chosen.	Suppose, for
     example, that you want to place buffer zones around roads.
     This program could create the raster map layer shown below
     on the right based on road information contained in the
     raster map layer shown on the left.

     000000000000000000000000	222233333333333333444444
     111000000000000000000000	111222222222223333333333
     000111111111100000000000	222111111111122223333333
     000000001000011100000000	332222221222211122222222
     000000001000000011111111	333333321233222211111111
     000000001000000000000000	433333321233333222222222
     000000001000000000000000	444443321233333333333333
     000000001000000000000000	444443321233443333333333
     000000001000000000000000	444443321233444444444444
     Category 0: No roads	Category 1: Road location
     Category 1: Roads		Category 2: Buffer Zone 1 around roads
				Category 3: Buffer Zone 2 around roads
				Category 4: Buffer Zone 3 around roads

INTERACTIVE PROGRAM USE
     The user can run the program interactively by simply typing
     r.buffer without program arguments on the command line.  The
     program then prompts the user for parameter values.

     (1) You are requested to identify the existing raster map
     layer from which distance-from calculations shall be based,
     and a name (of your choice) for the new raster map layer
     which will contain the results.

     (2) Then, identify the units of measurement in which buffer
     (distance) zones are to be calculated, and the distance of
     each buffer zone from each non-zero cell in the input map.
     The user has the option of identifying up to 60 continuous
     zones.  The zones are identified by specifying the upper
     limit of each desired zone (r.buffer assumes that 0 is the



GRASS 5.0beta6	      GRASS Development Team			1






r.buffer <main>	      GRASS Reference Manual	  <main> r.buffer



     starting point).  ("Continuous" is used in the sense that
     each category zone's lower value is the previous zone's
     upper value.  The first buffer zone always has distance 0 as
     its lower bound.)	Distances can be entered in one of four
     units:  meters, kilometers, feet, and miles.

     (3) Last, calculate distances from cells containing user-
     specified category values, using the "fromcell" method.
     [The "fromcell" method goes to each cell that contains a
     category value from which distances are to be calculated,
     and draws the requested distance rings around them.  This
     method works very fast when there are few cells containing
     the category values of interest, but works slowly when there
     are numerous cells containing the category values of
     interest spread throughout the area.]



NON-INTERACTIVE PROGRAM USE
     The user can run r.buffer specifying all parameter values on
     the command line, using the form:

	  r.buffer [-q] input=name output=name
	     distances=value[,value,...]  [units=name]


     Flags:

     -q	  Run quietly


     Parameters:

     input=name	       The name of an existing raster map layer
		       whose non-zero category value cells are to
		       be surrounded by buffer zones in the
		       output map.

     output=name       The name assigned to the new raster map
		       layer containing program output.	 The
		       output map will contain buffer zones at
		       the user-specified distances from non-zero
		       category value cell in the input map.

     distances=value[,value,...]
		       The distance of each buffer zone from
		       cells having non-zero category values in
		       the input map.

     units=name	       The unit of measurement in which distance
		       zone values are to be calculated.
		       Possible choices for name are: meters,



2		      GRASS Development Team	   GRASS 5.0beta6






r.buffer <main>	      GRASS Reference Manual	  <main> r.buffer



		       kilometers, feet, and miles.  The default
		       units used, if unspecified by the user,
		       are meters.

EXAMPLE
     In the example below, the buffer zones would be (in the
     default units of meters): 0-10, 11-20, 21-30, 31-40 and
     41-50.

	  Format:
	  r.buffer  input=name	output=name  distances=value[,value,...]  [units=name]

	  Example:
	  r.buffer  input=map.in  output=map.out  distances=10,20,30,40,50  units=meters

NOTES
     r.buffer measures distances from center of cell to center of
     cell using Euclidean distance measure for planimetric
     databases (like UTM) and using ellipsoidal geodesic distance
     measure for latitude/longitude databases.

     r.buffer calculates distance zones from all cells having
     non-zero category values in the input map.	 If the user
     wishes to calculate distances from only selected input map
     layer category values, the user should run (for example)
     r.reclass prior to r.buffer, to reclass all categories from
     which distance zones are not desired to be calculated into
     category zero.

SEE ALSO
     r.region, r.mapcalc, r.reclass

AUTHORS
     Michael Shapiro, U.S. Army Construction Engineering Research
     Laboratory
     James Westervelt, U.S. Army Construction Engineering
     Research Laboratory


















GRASS 5.0beta6	      GRASS Development Team			3