NAME

       r.fillnulls  - Fills no-data areas in raster maps using spline interpolation.

KEYWORDS

       raster, elevation, interpolation

SYNOPSIS

       r.fillnulls
       r.fillnulls help
       r.fillnulls  input=string  output=string   [tension=float]   [smooth=float]  method=string  [--overwrite]
       [--verbose]  [--quiet]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=string
           Name of input raster map in which to fill nulls

       output=string
           Name for output raster map with nulls filled by interpolation

       tension=float
           Spline tension parameter
           Default: 40.

       smooth=float
           Spline smoothing parameter
           Default: 0.1

       method=string
           Interpolation method
           Options: bilinear,bicubic,rst
           Default: rst

DESCRIPTION

       r.fillnulls fills NULL pixels (no data areas) in input map and stores filled map to a new output map. The
       fill data are interpolated from the no data area boundaries buffer  using  v.surf.rst  or  v.surf.bspline
       interpolation.

NOTES

       Each  area  boundary buffer is set to three times the map resolution to get nominally three points around
       the edge. This way the algorithm interpolates into the hole with a trained slope  and  curvature  at  the
       edges, in order to avoid that such a flat plane is generated in a hole.

       During the interpolation following warning may occur when using the RST method:

       Warning: strip exists with insufficient data
       Warning:  taking  too  long to find points for interpolation--please change the region to area where your
       points are

       This warning is generated if large data holes exist within the surface.  As the idea of r.fillnulls is to
       fill such holes, the user may ignore the warning. The interpolation will be continued. However, the  user
       may pay attention to below notes.

NOTES

       When  using the default RST method, the algorithm is based on v.surf.rst regularized splines with tension
       interpolation module which interpolates the raster cell values for NULL  data  areas  from  the  boundary
       values  of the NULL data area. An eventual raster MASK is respected during the NULL data area(s) filling.
       The interpolated values are patched into the NULL data area(s) of the input map  and  saved  into  a  new
       raster map.  Otherwise, either the bilinear or bicubic method can be selected (based on v.surf.bspline).

WARNING

       Depending on the shape of the NULL data area(s) problems may occur due to an insufficient number of input
       cell  values  for the interpolation process. Most problems will occur if a NULL data area reaches a large
       amount of the map boundary. The user will have to carefully check the result using r.mapcalc  (generating
       a  difference  map  to  the  input  map  and applying the "differences" color table with r.colors) and/or
       d.what.rast to query individual cell values.

EXAMPLE

       In this example, the SRTM elevation map in the North Carolina sample dataset  location  is  filtered  for
       outlier elevation values; missing pixels are then re-interpolated to obtain a complete elevation map:
       g.region rast=elev_srtm_30m -p
       d.mon x0
       d.histogram elev_srtm_30m
       # remove too low elevations (esp. lakes)
       r.mapcalc "elev_srtm_30m_filt = if(elev_srtm_30m < 50.0, null(), elev_srtm_30m)"
       d.histogram elev_srtm_30m_filt
       d.rast elev_srtm_30m_filt
       r.fillnulls input=elev_srtm_30m_filt output=elev_srtm_30m_complete tension=20
       d.histogram elev_srtm_30m_complete
       d.rast elev_srtm_30m_complete

SEE ALSO

        r.fill.dir, r.mapcalc, v.surf.bspline, v.surf.rst

REFERENCES

        Mitas,  L.,  Mitasova,  H.,  1999,  Spatial  Interpolation. In: P.Longley, M.F. Goodchild, D.J. Maguire,
       D.W.Rhind (Eds.), Geographical Information Systems: Principles, Techniques, Management and  Applications,
       Wiley, pp.481-492

       Mitasova  H.,  Mitas L.,  Brown W.M.,  D.P. Gerdes, I.  Kosinovsky, Baker, T.1995, Modeling spatially and
       temporally distributed phenomena: New methods and tools for GRASS GIS. International Journal  of  GIS,  9
       (4), special issue on Integrating GIS and Environmental modeling, 433-446.

       Mitasova  H.   and  Mitas  L.  1993:  Interpolation  by  Regularized  Spline with Tension: I.  Theory and
       Implementation, Mathematical Geology 25, 641-655.

       Mitasova H.  and Hofierka L. 1993: Interpolation by Regularized Spline with Tension: II.  Application  to
       Terrain Modeling and Surface Geometry Analysis, Mathematical Geology 25, 657-667.

AUTHORS

       r.fillnulls: Markus Neteler, University of Hannover and Fondazione Edmund Mach

       and authors of v.surf.rst
       Improvement by Hamish Bowman, NZ

       Last changed: $Date: 2012-03-04 03:55:32 -0800 (Sun, 04 Mar 2012) $

       Full index

       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                  r.fillnulls(1grass)