sphinterpolate
sphinterpolate - Spherical gridding in tension of data on a sphere
sphinterpolate [ table ] -Ggrdfile
[ -Iincrement ]
[ -Qmode[/options] ]
[ -Rregion ]
[ -V[level] ]
[ -Z ]
[ -bi<binary> ]
[ -di<nodata> ]
[ -h<headers> ]
[ -i<flags> ]
[ -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, f 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][=|+][/yinc[unit][=|+]]
- 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,
nautical mile or US survey foot, respectively, and will be converted to
the equivalent degrees longitude at the middle latitude 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 coordinates: If = 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 + to the supplied integer argument; the increment is then
recalculated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a
gridline-registered or pixel-registered grid; see GMT 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 preserve
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
tensions are selected (e.g., -T only) [3], M is the number of
Gauss-Seidel iterations used when determining the global gradients
[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.
- -R[unit]west/east/south/north[/zmin/zmax][r]
- west, east, south, and north specify the region of interest,
and you may specify them in decimal degrees or in
[+-]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. Using -Runit expects projected (Cartesian)
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 ...)
- Select verbosity level [c].
- -Z
- Before interpolation, scale data by the maximum data range [no
scaling].
- -bi[ncols][t] (more ...)
- Select native binary input. [Default is 3 input columns].
- -dinodata (more ...)
- Replace input columns that equal nodata with NaN.
- -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
- Skip or produce header record(s).
- -:[i|o] (more ...)
- Swap 1st and 2nd column on input and/or output.
- -r (more ...)
- Set pixel node registration [gridline].
- -^ or just -
- Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
- -+ or just +
- Print an extensive usage (help) message, including the explanation 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
options, then exits.
- --version
- Print GMT version and exit.
- --show-datadir
- Print full path to GMT share directory and exit.
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
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.