xenial (1) sphinterpolate.1gmt.gz
NAME
sphinterpolate - Spherical gridding in tension of data on a sphere
SYNOPSIS
sphinterpolate [ table ] grdfile [ increment ] [ mode[/options] ] [ region ] [ [level] ] [ ] [
-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 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 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.
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, whereas other values are formatted according to
FORMAT_FLOAT_OUT. Be aware that the format in effect can lead to loss of precision in the 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 setting.
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, greenspline, nearneighbor, sphdistance, sphtriangulate, surface, triangulate
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
2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe