r.resamp.rst(1grass) GRASS GIS User's Manual r.resamp.rst(1grass)
NAME
r.resamp.rst - Reinterpolates and optionally computes topographic
analysis from input raster map to a new raster map (possibly with dif-
ferent resolution) using regularized spline with tension and smoothing.
KEYWORDS
raster, resample, splines, RST
SYNOPSIS
r.resamp.rst
r.resamp.rst --help
r.resamp.rst [-td] input=name ew_res=float ns_res=float [eleva-
tion=name] [slope=name] [aspect=name] [pcurvature=name] [tcur-
vature=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 how-
ever has to be aligned to the resolution of the input map to avoid
artefacts.
Reinterpolation (resampling) is done to higher, same or lower resolu-
tion 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 parame-
ters are computed from an input raster map containing z-values of ele-
vation/depth: slope, aspect, profile curvature (measured in the direc-
tion of steepest slope), tangential curvature (measured in the direc-
tion of a tangent to contour line) and/or mean curvature are computed
from and saved as raster maps as specified by the options slope, as-
pect, 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 me-
ters, so that the proper values of slopes and curvatures can be com-
puted. 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 de-
sired 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. us-
ing 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 result-
ing 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 computa-
tion of values at given points, and prints the maximum difference found
into the history file of raster map elev (view with r.info). An in-
crease 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 follow-
ing 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 in-
fluences 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 Informa-
tion Systems: Principles, Techniques, Management and Applications, Wi-
ley, 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 Re-
gional Conference series in applied mathematics, 59, SIAM, Philadel-
phia, Pennsylvania.
SOURCE CODE
Available at: r.resamp.rst source code (history)
Accessed: unknown
Main index | Raster index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 r.resamp.rst(1grass)
Generated by dwww version 1.14 on Sun Apr 20 08:05:47 CEST 2025.