Provided by: grass-doc_6.4.3-3_all 
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.
SEE ALSO
g.region, r.info, r.resample, r.mapcalc, r.surf.contour, v.surf.rst
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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