xenial (1) sphinterpolate.1gmt.gz

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

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.

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe