Ubuntu Manpage: r.resamp.rst - Reinterpolates and optionally computes topographic analysis from input raster map to a

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  [elev=string]   [slope=string]   [aspect=string]
       [pcurv=string]   [tcurv=string]   [mcurv=string]   [smooth=string]   [maskmap=string]   [overlap=integer]
       [zmult=float]   [tension=float]   [theta=float]   [scalex=float]   [--overwrite]  [--verbose]  [--quiet]

   Flags:
       -t
           Use dnorm independent tension

       -d
           Output partial derivatives instead of topographic parameters

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input raster map

       ew_res=float
           Desired east-west resolution

       ns_res=float
           Desired north-south resolution

       elev=string
           Output z-file (elevation) map

       slope=string
           Output slope map (or fx)

       aspect=string
           Output aspect map (or fy)

       pcurv=string
           Output profile curvature map (or fxx)

       tcurv=string
           Output tangential curvature map (or fyy)

       mcurv=string
           Output mean curvature map (or fxy)

       smooth=string
           Name of raster map containing smoothing

       maskmap=string
           Name of raster map to be used as mask

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

       zmult=float
           Multiplier for z-values
           Default: 1.0

       tension=float
           Spline tension value
           Default: 40.

       theta=float
           Anisotropy angle (in degrees)

       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). 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.

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: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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       © 2003-2013 GRASS Development Team

GRASS 6.4.3                                                                                 r.resamp.rst(1grass)