Provided by: gmt-common_5.4.5+dfsg-1_all bug

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, 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 +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 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.

       -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 [±]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 (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.

       -e[~]"pattern" | -e[~]/regexp/[i] (more ...)
              Only accept data records that match the given pattern.

       -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
              just use -).

       -+ 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  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 FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format 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 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

       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe