Provided by: gmt_4.5.11-1build1_amd64 bug


       sphinterpolate - Gridding in tension of spherical data


       sphinterpolate     infiles     -Ggrdfile     [     -F     ]     [    -H[i][nrec]    ]    [
       -Ixinc[unit][=|+][/yinc[unit][=|+]] ] [ -Qmode[/options] ] [ -Rwest/east/south/north[r]  ]
       [ -V ] [ -Z ] [ -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ][ -m[i|o][flag] ]


       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.

              Data  files with the (lon, lat, f) coordinates in ASCII (or binary; see -b).  If no
              files are given the standard input is read.

       -G     Name of the output grid to hold the interpolation.


       -F     Force  pixel  node  registration  [Default  is   gridline   registration].    (Node
              registrations are defined in GMT Cookbook Appendix B on grid file formats.)

       -H     Input  file(s) has header record(s).  If used, the default number of header records
              is N_HEADER_RECS.  Use -Hi if only input data should have header  records  [Default
              will  write  out header records if the input data have them]. Blank lines and lines
              starting with # are always skipped.

       -I     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
              c to indicate arc seconds.  If one of the units e, k, i, or n is appended  instead,
              the  increment  is  assumed  to  be  given  in meter, km, miles, or nautical miles,
              respectively, and will be converted to the  equivalent  degrees  longitude  at  the
              middle  latitude of the region (the conversion depends on 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
              Appendix B for details.  Note: if -Rgrdfile is used then grid spacing  has  already
              been initialized; use -I to override the values.

       -Q     Specify  one  of  four  ways  to  calculate tension factors to preserve local shape
              properties or satisfy arc constraints [Default is no tension].

       -Q 0   Piecewise linear interpolation; no tension is applied.

       -Q 1   Smooth interpolation with local gradient estimates.

       -Q 2   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].

       -Q 3   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     west, east, south, and north specify the Region of interest, and  you  may  specify
              them  in  decimal  degrees  or  in [+-]dd:mm[][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,  specify  the  name  of  an
              existing grid file and the -R settings (and grid spacing, if applicable) are copied
              from the grid.

       -T     Use variable tension (ignored with -Q 0 [constant]

       -V     Selects verbose mode, which will send progress  reports  to  stderr  [Default  runs

       -Z     Before interpolation, scale data by the maximum data range [no scaling].

       -:     Toggles  between (longitude,latitude) and (latitude,longitude) input and/or output.
              [Default is (longitude,latitude)].  Append i to select input only or  o  to  select
              output only.  [Default affects both].

       -bi    Selects  binary  input.   Append  s  for  single precision [Default is d (double)].
              Uppercase S or D will force byte-swapping.  Optionally, append ncol, the number  of
              columns  in your binary input file if it exceeds the columns needed by the program.
              Or append c if the input  file  is  netCDF.  Optionally,  append  var1/var2/...  to
              specify the variables to be read.  [Default is 3 input columns].

       -bo    Selects  binary  output.   Append  s  for single precision [Default is d (double)].
              Uppercase S or D will force byte-swapping.  Optionally, append ncol, the number  of
              desired columns in your binary output file.  [Default is same as input].

       -m     Multiple  segment  file(s).  Segments are separated by a special record.  For ASCII
              files the first character must be flag [Default is  '>'].   For  binary  files  all
              fields  must  be  NaN  and -b must set the number of output columns explicitly.  By
              default the -m setting applies to both input and output.  Use -mi and -mo  to  give
              separate settings to input and output.


       The  ASCII  output  formats  of  numerical  data  are  controlled  by  parameters  in your
       .gmtdefaults4   file.    Longitude   and   latitude    are    formatted    according    to
       OUTPUT_DEGREE_FORMAT,  whereas other values are formatted according to D_FORMAT.  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
       D_FORMAT setting.


       Regardless  of  the  precision of the input data, GMT programs that create grid files will
       internally hold the grids in 4-byte floating point  arrays.   This  is  done  to  conserve
       memory and furthermore most if not all real data can be stored using 4-byte floating point
       values.  Data with higher  precision  (i.e.,  double  precision  values)  will  lose  that
       precision  once  GMT  operates  on  the  grid  or  writes out new grids.  To limit loss of
       precision when processing data you should always consider normalizing the  data  prior  to


       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.grd


       GMT(1), greenspline(1) sphdistance(1) sphtriangulate(1) triangulate(1)


       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),