xenial (1) r.fillnulls.1grass.gz

Provided by: grass-doc_7.0.3-1build1_all bug

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=name  output=name  method=string   [tension=float]    [smooth=float]    [edge=integer]
       [npmin=integer]   [segmax=integer]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

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

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input raster map

       output=name [required]
           Name for output raster map

       method=string [required]
           Interpolation method to use
           Options: bilinear, bicubic, rst
           Default: rst

       tension=float
           Spline tension parameter
           Default: 40.

       smooth=float
           Spline smoothing parameter
           Default: 0.1

       edge=integer
           Width of hole edge used for interpolation (in cells)
           Options: 2-100
           Default: 3

       npmin=integer
           Minimum number of points for approximation in a segment (>segmax)
           Options: 2-10000
           Default: 600

       segmax=integer
           Maximum number of points in a segment
           Options: 2-10000
           Default: 300

DESCRIPTION

       r.fillnulls fills NULL pixels (no data areas) in input raster map and stores filled data to a new  output
       raster  map.  The  fill  areas  are interpolated from the no data area boundaries buffer using v.surf.rst
       regularized spline interpolation with tension (method=rst) or r.resamp.bspline  cubic  or  linear  spline
       interpolation with Tykhonov regularization.

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. The width of edge area can be
       adjusted by changing the edge parameter.

       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.

       If  interpolation  fails,  temporary  raster and vector maps are left in place to allow unfilled map hole
       (NULL area) identification and manual repair.

       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 linear or cubic spline interpolation with Tykhonov regularization  can
       be selected (based on r.resamp.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  to
       query individual cell values.

       RST  method  stores temporary maps on hard disk. It will require at least as much free space as one extra
       input raster map takes.

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 raster=elev_srtm_30m -p
       d.mon wx0
       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

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.

SEE ALSO

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

AUTHORS

       Markus Neteler, University of Hannover  and Fondazione Edmund Mach
       Improvement by Hamish Bowman, NZ

       Last changed: $Date: 2015-12-31 09:19:51 +0100 (Thu, 31 Dec 2015) $

       Main index | Raster index | Topics index | Keywords index | Full index

       © 2003-2016 GRASS Development Team, GRASS GIS 7.0.3 Reference Manual