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NAME

       r.resamp.rst   -  Reinterpolates  and  optionally computes topographic analysis from input
       raster map to a new raster map (possibly  with  different  resolution)  using  regularized
       spline with tension and smoothing.

KEYWORDS

       raster, resample

SYNOPSIS

       r.resamp.rst
       r.resamp.rst --help
       r.resamp.rst  [-td]  input=name ew_res=float ns_res=float  [elevation=name]   [slope=name]
       [aspect=name]   [pcurvature=name]   [tcurvature=name]   [mcurvature=name]    [smooth=name]
       [maskmap=name]     [overlap=integer]    [zscale=float]    [tension=float]    [theta=float]
       [scalex=float]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -t
           Use dnorm independent tension

       -d
           Output partial derivatives instead of topographic parameters

       --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

       ew_res=float [required]
           Desired east-west resolution

       ns_res=float [required]
           Desired north-south resolution

       elevation=name
           Name for output elevation raster map

       slope=name
           Name for output slope map (or fx)

       aspect=name
           Name for output aspect map (or fy)

       pcurvature=name
           Name for output profile curvature map (or fxx)

       tcurvature=name
           Name for output tangential curvature map (or fyy)

       mcurvature=name
           Name for output mean curvature map (or fxy)

       smooth=name
           Name of input raster map containing smoothing

       maskmap=name
           Name of input raster map to be used as mask

       overlap=integer
           Rows/columns overlap for segmentation
           Default: 3

       zscale=float
           Multiplier for z-values
           Default: 1.0

       tension=float
           Spline tension value
           Default: 40.

       theta=float
           Anisotropy angle (in degrees counterclockwise from East)

       scalex=float
           Anisotropy scaling factor

DESCRIPTION

       r.resamp.rst reinterpolates the values a from given raster map  (named  input)  to  a  new
       raster  map  (named elev).  This module is intended for reinterpolation of continuous data
       to a different resolution rather than for  interpolation  from  scattered  data  (use  the
       v.surf.* modules for that purpose).

       The  extent  of  all  resulting  raster  maps  is  taken  from  the settings of the actual
       computational region (which may differ from the extent  of  the  input  raster  map).  The
       resolution  of the computational region however has to be aligned to the resolution of the
       input map to avoid artefacts.

       Reinterpolation (resampling) is done to higher, same or lower resolution specified by  the
       ew_res and ns_res parameters.

       All  resulting raster maps are created using the settings of the current region (which may
       be different from that of the input raster map).

       Optionally, and simultaneously with interpolation,  topographic  parameters  are  computed
       from  an  input  raster map containing z-values of elevation/depth: slope, aspect, profile
       curvature (measured in the direction of steepest slope), tangential curvature (measured in
       the  direction  of  a tangent to contour line) and/or mean curvature are computed from and
       saved as raster maps as specified by  the  options  slope,  aspect,  pcurv,  tcurv,  mcurv
       respectively.

       If  the  -d  flag is set the program outputs partial derivatives fx, fy, fxx, fxy, and fyy
       instead of slope, aspect and curvatures.

       For noisy data it is possible to define spatially variable smoothing by providing a raster
       map  named  by  the  smooth  option  containing  smoothing parameters.  With the smoothing
       parameter set to zero (smooth is not given or contains zero data), the  resulting  surface
       passes exactly through the data points.

       The  user  can also define a raster map (named with maskmap) which will be used as a mask.
       The interpolation is skipped for cells which have zero or NULL value in the mask.

       Zero values will be assigned to these cells in all output raster maps.

       The zmult parameter allows the user to rescale the z-values which may be useful, e.g., for
       transformation  of elevations given in feet to meters, so that the proper values of slopes
       and curvatures can be computed.  The default value is 1.

       A regularized spline with tension method is  used  for  the  interpolation.   The  tension
       parameter tunes the character of the resulting surface from thin plate to membrane. Higher
       values of tension parameter reduce the overshoots that can appear in surfaces  with  rapid
       change of gradient.

       The -t flag can be set to use "dnorm independent tension".

       The  interpolation is performed for overlapping rectangular segments.  The user can define
       the width of overlap (in number of cells) with the overlap option. The default value is 3.

NOTES

       r.resamp.rst uses regularized spline with  tension  for  interpolation  (as  described  in
       Mitasova and Mitas, 1993).

       The  region  is  temporarily  changed  while writing output files with desired resolution.
       Topographic parameters are computed in the same way as in the v.surf.rst module. (See also
       Mitasova and Hofierka, 1993)

       The  raster  map used with the smooth option should contain variable smoothing parameters.
       These can be derived from errors, slope, etc. using the r.mapcalc module.

       The program gives warning when significant overshoots appear and higher tension should  be
       used.  However,  with tension set too high the resulting surface changes its behavior to a
       membrane (rubber sheet stretched over the data points resulting in a peak or pit  in  each
       given  point and everywhere else the surface goes rapidly to trend). Smoothing can be used
       to reduce the overshoots. When overshoots occur the resulting elev file  will  have  white
       color in the locations of overshoots since the color table for the output file is the same
       as colortable for raster input file.

       The program checks the numerical stability of the algorithm by computation  of  values  at
       given  points, and prints the maximum difference found into the history file of raster map
       elev (view with r.info).  An increase  in  tension  is  suggested  if  the  difference  is
       unacceptable.  For computations with smoothing set to 0 this difference should be 0.  With
       a smoothing parameter greater than zero the surface will not pass through the data  points
       exactly, and the higher the parameter the closer the surface will be to the trend.

       The  program  writes the values of parameters used in computation into the comment part of
       the elev map history file. Additionally the following values are also written to assist in
       the evaluation of results and choosing of suitable parameters:

           ·   minimum  and  maximum  z values in the data file (zmin_data, zmax_data) and in the
               interpolated raster map (zmin_int, zmax_int),

           ·   maximum difference between the given and interpolated z value  at  a  given  point
               (errtotal),

           ·   rescaling parameter used for normalization (dnorm), which influences the tension.

       The program gives a warning when the user wants to interpolate outside the region given by
       the input raster map’s header data.  Zooming  into  the  area  where  the  points  are  is
       suggested in this case.

       When  a  mask  is used, the program uses all points in the given region for interpolation,
       including those in the area which is masked out, to ensure proper interpolation along  the
       border  of the mask. It therefore does not mask out the data points; if this is desirable,
       it must be done outside r.resamp.rst before processing.

EXAMPLE

       Resampling the Spearfish 30m resolution elevation model to 15m:
       # set computation region to original map (30m)
       g.region raster=elevation.dem -p
       # resample to 15m
       r.resamp.rst input=elevation.dem ew_res=15 ns_res=15 elevation=elev15
       # set computation region to resulting map
       g.region raster=elev15 -p
       # verify
       r.univar elev15 -g

SEE ALSO

       g.region, r.info, r.resample, r.mapcalc, r.surf.contour, v.surf.rst

       Overview: Interpolation and Resampling in GRASS GIS

AUTHORS

       Original version of program (in FORTRAN):
       Lubos Mitas, NCSA, University of Illinois at Urbana Champaign, Il
       Helena Mitasova, US Army CERL, Champaign, Illinois

       Modified program (translated to C, adapted for GRASS , segmentation procedure):
       Irina Kosinovsky, US Army CERL.
       Dave Gerdes, US Army CERL.

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, 481-492.

       Mitasova, H. and Mitas, L., 1993. Interpolation by regularized  spline  with  tension:  I.
       Theory and implementation, Mathematical Geology No.25 p.641-656.

       Mitasova, H. and Hofierka, L., 1993. Interpolation by regularized spline with tension: II.
       Application to terrain modeling and surface geometry analysis, Mathematical Geology  No.25
       p.657-667.

       Talmi,  A.  and  Gilat,  G.,  1977.  Method  for  smooth approximation of data, Journal of
       Computational Physics , 23, pp 93-123.

       Wahba, G., 1990. Spline models for observational data, CNMS-NSF Regional Conference series
       in applied mathematics, 59, SIAM, Philadelphia, Pennsylvania.

       Last changed: $Date: 2016-08-03 13:50:26 +0200 (Wed, 03 Aug 2016) $

SOURCE CODE

       Available at: r.resamp.rst source code (history)

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