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       r.bilinear  - Bilinear interpolation utility for raster map layers.


       raster, resample


       r.bilinear help
       r.bilinear    input=name   output=name    [north=float]     [east=float]     [--overwrite]
       [--verbose]  [--quiet]

           Allow output files to overwrite existing files

           Verbose module output

           Quiet module output

           Name of input raster map

           Name for output raster map

           Specific input value to be assigned to the north and/or  south  poles  for  longitude-
           latitude grids

           Specific  input  value  to  be assigned to the north and/or south poles for longitude-
           latitude grids


   This module is deprecated and scheduled for demolition.
       Please use "r.resamp.interp" instead.  r.bilinear fills a grid cell (raster)  matrix  with
       interpolated values generated from a set of input layer data points.  It uses the bilinear
       interpolation method, a simple algorithm usually applied only to completely defined raster
       areas (input data void of null data values).  Here the values of 4 input cells are used to
       define an interpolation function of constant gradient within each rectangular area defined
       by  the  cell  centers.   User  should  be  aware  that  the gradient of the interpolation
       functions changes discontinuously across lines intersecting the cell centers of the  input

       If there is a current working mask, it applies to the output raster map.  Only those cells
       falling within the mask will be assigned interpolated values.  The procedure for selection
       of  input  data  will consider all input data relevant to interpolating values at the cell
       centers of the current geographic region, ignoring the curent mask.  Note  that  cells  of
       the output raster that cannot be bounded by 4 input cell centers are set to null.


       The north and south parameters have been included to allow for specific input values to be
       assigned to the north and/or south poles for longitude-latitude  grids.   These  data,  if
       included,  are  used  to  interpolate  values  for cells that are north or south of a line
       intersecting the cell centers of the first or  last  row  of  input,  respectively.   When
       utilized,  the  interpolation  procedure  will  be  continuous from the north and/or south
       boundary of the current geographic region.  This  option  is  necessary,  since  the  data
       structure  defining  a raster will not allow for data to be assigned to a cell centered at
       90N or 90S.  By including the option,  the  user  can  create  output  surfaces  that  are
       continuous  between  the poles.  The interpolation will be "wrap-around" from west to east
       (across latitude) only if the input raster has an east edge identical to its west edge.

       For  longitude-latitude  databases,  the  interpolation  algorithm  is  based  on   degree
       fractions,  not  on the absolute distances between cell centers.  Any attempt to implement
       the latter would violate the integrity of the interpolation method.

       r.bilinear may be used in some  instances  as  an  alternative  to  the  nearest  neighbor
       approach  inherent to r.resample.  Note, however, that the extent of non-null data area of
       the output raster must be less than that of the input raster.  The only exception to  this
       occurs  in  the  case  where  the  north  and south parameters are utilized for longitude-
       latitude rasters.

SEE ALSO,, g.region, r.resample, r.resamp.interp, r.resamp.stats


       Greg Koerper
       ManTech Environmental Technology, Inc.
       Global Climate Research Project
       U.S. EPA Environmental Research Laboratory

       Last changed: $Date: 2010-01-20 05:26:08 -0800 (Wed, 20 Jan 2010) $

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