sphinterpolate(1) GMT sphinterpolate(1)
NAME
sphinterpolate - Spherical gridding in tension of data on a sphere
SYNOPSIS
sphinterpolate [ table ] -Ggrdfile [ -Iincrement ] [
-Qmode[/options] ] [ -Rregion ] [ -V[level] ] [ -Z ] [ -bibinary ] [
-dinodata ] [ -eregexp ] [ -hheaders ] [ -iflags ] [ -r ] [ -:[i|o] ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
sphinterpolate reads one or more ASCII [or binary] files (or standard
input) containing lon, lat, z and performs a Delaunay triangulation to
set up a spherical interpolation in tension. The final grid is saved to
the specified file. Several options may be used to affect the outcome,
such as choosing local versus global gradient estimation or optimize
the tension selection to satisfy one of four criteria.
REQUIRED ARGUMENTS
-Ggrdfile
Name of the output grid to hold the interpolation.
OPTIONAL ARGUMENTS
table One or more ASCII (or binary, see -bi[ncols][type]) data table
file(s) holding a number of data columns. If no tables are given
then we read from standard input.
-Ixinc[unit][+e|n][/yinc[unit][+e|n]]
x_inc [and optionally y_inc] is the grid spacing. Optionally,
append a suffix modifier. Geographical (degrees) coordinates:
Append m to indicate arc minutes or s to indicate arc seconds.
If one of the units e, f, k, M, n or u is appended instead, the
increment is assumed to be given in meter, foot, km, Mile, nau-
tical mile or US survey foot, respectively, and will be con-
verted to the equivalent degrees longitude at the middle lati-
tude of the region (the conversion depends on PROJ_ELLIPSOID).
If y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordi-
nates: If +e is appended then the corresponding max x (east) or
y (north) may be slightly adjusted to fit exactly the given
increment [by default the increment may be adjusted slightly to
fit the given domain]. Finally, instead of giving an increment
you may specify the number of nodes desired by appending +n to
the supplied integer argument; the increment is then recalcu-
lated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a grid-
line-registered or pixel-registered grid; see App-file-formats
for details. Note: if -Rgrdfile is used then the grid spacing
has already been initialized; use -I to override the values.
-Qmode[/options]
Specify one of four ways to calculate tension factors to pre-
serve local shape properties or satisfy arc constraints [Default
is no tension].
-Q0 Piecewise linear interpolation; no tension is applied.
-Q1 Smooth interpolation with local gradient estimates.
-Q2 Smooth interpolation with global gradient estimates. You may
optionally append /N/M/U, where N is the number of iterations
used to converge at solutions for gradients when variable ten-
sions are selected (e.g., -T only) [3], M is the number of
Gauss-Seidel iterations used when determining the global gradi-
ents [10], and U is the maximum change in a gradient at the last
iteration [0.01].
-Q3 Smoothing. Optionally append /E/U [/0/0], where E is Expected
squared error in a typical (scaled) data value, and U is Upper
bound on weighted sum of squares of deviations from data.
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]
west, east, south, and north specify the region of interest, and
you may specify them in decimal degrees or in
[A+-]dd:mm[:ss.xxx][W|E|S|N] format Append +r if lower left and
upper right map coordinates are given instead of w/e/s/n. The
two shorthands -Rg and -Rd stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in latitude).
Alternatively for grid creation, give Rcodelon/lat/nx/ny, where
code is a 2-character combination of L, C, R (for left, center,
or right) and T, M, B for top, middle, or bottom. e.g., BL for
lower left. This indicates which point on a rectangular region
the lon/lat coordinate refers to, and the grid dimensions nx and
ny with grid spacings via -I is used to create the corresponding
region. Alternatively, specify the name of an existing grid
file and the -R settings (and grid spacing, if applicable) are
copied from the grid. Appending +uunit expects projected (Carte-
sian) coordinates compatible with chosen -J and we inversely
project to determine actual rectangular geographic region. For
perspective view (-p), optionally append /zmin/zmax. In case of
perspective view (-p), a z-range (zmin, zmax) can be appended to
indicate the third dimension. This needs to be done only when
using the -Jz option, not when using only the -p option. In the
latter case a perspective view of the plane is plotted, with no
third dimension.
-T Use variable tension (ignored with -Q0 [constant]
-V[level] (more a|)
Select verbosity level [c].
-Z Before interpolation, scale data by the maximum data range [no
scaling].
-bi[ncols][t] (more a|)
Select native binary input. [Default is 3 input columns].
-dinodata (more a|)
Replace input columns that equal nodata with NaN.
-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
Only accept data records that match the given pattern.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s).
-:[i|o] (more a|)
Swap 1st and 2nd column on input and/or output.
-r (more a|)
Set pixel node registration [gridline].
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion of any module-specific option (but not the GMT common
options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation
of all options, then exits.
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters
in your gmt.conf file. Longitude and latitude are formatted according
to FORMAT_GEO_OUT, absolute time is under the control of FOR-
MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val-
ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
mat in effect can lead to loss of precision in ASCII output, which can
lead to various problems downstream. If you find the output is not
written with enough precision, consider switching to binary output (-bo
if available) or specify more decimals using the FORMAT_FLOAT_OUT set-
ting.
EXAMPLES
To interpolate the points in the file testdata.txt on a global 1x1
degree grid with no tension, use
sphinterpolate testdata.txt -Rg -I1 -Gsolution.nc
SEE ALSO
gmt(1), greenspline(1), nearneighbor(1), sphdistance(1),
sphtriangulate(1), surface(1), triangulate(1)
REFERENCES
Renka, R, J., 1997, Algorithm 772: STRIPACK: Delaunay Triangulation and
Voronoi Diagram on the Surface of a Sphere, AMC Trans. Math. Software,
23(3), 416-434.
Renka, R, J,, 1997, Algorithm 773: SSRFPACK: Interpolation of scattered
data on the Surface of a Sphere with a surface under tension, AMC
Trans. Math. Software, 23(3), 435-442.
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 sphinterpolate(1)
gmt5 5.4.2 - Generated Thu Jun 29 16:32:16 CDT 2017