Provided by: gmt-common_5.2.1+dfsg-3build1_all 
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