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.
EXAMPLE¶
Resampling the Spearfish 30m resolution elevation model to 15m:
# set computation region to original map (30m)
g.region rast=elevation.dem -p
# resample to 15m
r.resamp.rst input=elevation.dem ew_res=15 ns_res=15 elev=elev15
# set computation region to resulting map
g.region rast=elev15 -p
# verify
r.univar elev15 -g
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: 2014-04-20 19:36:58 +0200 (Sun, 20 Apr 2014) $
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