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sphinterpolate(1)                     GMT                    sphinterpolate(1)




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, nau-
              tical mile or US survey foot, respectively,  and  will  be  con-
              verted  to  the equivalent degrees longitude at the middle lati-
              tude 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  coordi-
              nates:  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  recalcu-
              lated  from  the  number  of nodes and the domain. The resulting
              increment value depends on whether you  have  selected  a  grid-
              line-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 pre-
              serve 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 ten-
              sions are selected (e.g., -T only)  [3],  M  is  the  number  of
              Gauss-Seidel  iterations used when determining the global gradi-
              ents [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
              [A+-]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 (Carte-
              sian) 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 a|)
              Select verbosity level [c].

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

       -bi[ncols][t] (more a|)
              Select native binary input. [Default is 3 input columns].

       -dinodata (more a|)
              Replace input columns that equal nodata with NaN.

       -e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
              Only accept data records that match the given pattern.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
              Skip or produce header record(s).

       -:[i|o] (more a|)
              Swap 1st and 2nd column on input and/or output.

       -r (more a|)
              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 explana-
              tion 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   FOR-
       MAT_DATE_OUT  and FORMAT_CLOCK_OUT, whereas general floating point val-
       ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
       mat  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  set-
       ting.


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(1), greenspline(1), nearneighbor(1), sphdistance(1),
       sphtriangulate(1), surface(1), triangulate(1)


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

       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe



5.4.2                            Jun 24, 2017                sphinterpolate(1)

gmt5 5.4.2 - Generated Thu Jun 29 16:32:16 CDT 2017
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