Provided by: gmt-common_5.4.3+dfsg-1_all bug


       gpsgridder   -  Interpolate  GPS  strain  vectors  using  Green's  functions  for  elastic


       gpsgridder [ table ]
        -Goutfile [  -Iincrement ] [  -Rregion ] [  -C[n|r|v]value[+ffile] ] [  -E[misfitfile]  ]
       [   -F[d|f]fudge]  [   -L  ]  [   -Nnodefile  ] [  -Snu ] [  -Tmaskgrid ] [  -V[level] ] [
       -W[w]] [ -bbinary ] [ -dnodata ] [ -eregexp ] [ -fflags ] [ -hheaders  ]  [  -oflags  ]  [
       -x[[-]n] ] [ -:[i|o] ]

       Note: No space is allowed between the option flag and the associated arguments.


       gpsgridder  grids 2-D vector data such as GPS velocities by using a coupled model based on
       2-D elasticity.  The degree of coupling can be tuned by adjusting the effective  Poisson’s
       ratio.  The  solution  field  can be tuned to extremes such as incompressible (1), typical
       elastic (0.5) or even an unphysical  value  of  -1  that  basically  removes  the  elastic
       coupling  of  vector  interpolation.  Smoothing is offered via the optional elimination of
       small eigenvalues.


       table  table with GPS strain rates at discrete locations.  We expect the input  format  to
              be x y u v [ du dv ] (see -W to specify data uncertainties or weights).  If lon lat
              is given you must supply -fg and we will use a  flat  Earth  approximation  in  the
              calculation of distances.

              Name  of  resulting  output file. (1) If options -R, -I, and possibly -r are set we
              produce two equidistant output grids. In this case, outfile must be a name template
              containing  the  C  format  specifier  %s,  which  will  be  replaced with u and v,
              respectively.  (2) If option -T is selected then -R, -I  cannot  be  given  as  the
              maskgrid  determines  the  region and increments. Again, the outfile must be a name
              template for the two output grids.  (3) If -N is selected  then  the  output  is  a
              single ASCII (or binary; see -bo) table written to outfile; if -G is not given then
              this table is written to standard output. The -G option is ignored if -C or -C0  is


              Find   an  approximate  surface  fit:  Solve  the  linear  system  for  the  spline
              coefficients by SVD and eliminate the contribution from all eigenvalues whose ratio
              to the largest eigenvalue is less than value [Default uses Gauss-Jordan elimination
              to solve the linear system and fit the data exactly]. Optionally, append +ffile  to
              save the eigenvalue ratios to the specified file for further analysis.  Finally, if
              a negative value is given then +ffile is required and  execution  will  stop  after
              saving  the  eigenvalues, i.e., no surface output is produced.  Specify -Cvvalue to
              use the largest eigenvalues needed  to  explain  value  %  of  the  data  variance.
              Specify -Crvalue to use the largest eigenvalues needed to leave approximately value
              as the model misfit.  If value is not given then -W  is  required  and  we  compute
              value  as  the rms of the given data uncertainties.  Alternatively, use -Cnvalue to
              select the value largest eigenvalues.  If a file is given with -Cv then we save the
              eigenvalues  instead  of  the  ratios.   Note:  1/4  of  the  total  number of data
              constraints is a good starting point for further experiments.

          Evaluate the spline exactly at the input data locations and report  statistics  of  the
          misfit  (mean,  standard  deviation,  and  rms)  for  u  and v separately and combined.
          Optionally, append a filename and we will write the data table, augmented by two  extra
          columns after each of the u and v columns holding the spline estimates and misfits.

              The Green’s functions are proportional to terms like 1/r^2 and log(r) and thus blow
              up for r == 0.  To prevent that we offer two fudging  schemes:  -Fddel_radius  lets
              you  add  a  constant  offset to all radii and must be specified in the user units.
              Alternatively, use -Fffactor which will compute del_radius from the product of  the
              shortest inter-point distance and factor [0.01].

              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.

       -L     Leave trend alone.  Do not remove a planer (2-D) trend from the data before fitting
              the spline.  [Default removes least squares plane, fits normalized  residuals,  and
              restores plane].

              ASCII  file  with coordinates of desired output locations x in the first column(s).
              The resulting w values are appended to each record and written to the file given in
              -G  [or  stdout  if  not specified]; see -bo for binary output instead. This option
              eliminates the need to specify options -R, -I, and -r.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
              Specify the region of interest.

       -Snu   Specify Poisson’s ratio to use for this 2-D elastic  sheet  [0.5].   Note:  1.0  is
              incompressible  in  a 2-D formulation while -1 removes all coupling between the two

              Only evaluate the solutions at the nodes in the maskgrid that are not set  to  NaN.
              This option eliminates the need to specify options -R, -I (and -r).

       -W[w]  One-sigma  data uncertainties for u and v are provided in the last two columns.  We
              then compute weights that are inversely proportional to the uncertainties.   Append
              w  if weights are given instead of uncertainties.  This results in a weighted least
              squares fit.  Note that -W only has an effect if -C  is  used.   [Default  uses  no
              weights  or uncertainties].  Note: At present the -W option is unstable.  We do not
              yet know if it reflects a coding bug or a theoretical  limitation.   Users  beware,
              and  make  sure  you  compare the results with non-weighted output for basic sanity

       -V[level] (more …)
              Select verbosity level [c].

       -d[i|o]nodata (more …)
              Replace input columns that equal nodata with NaN and do the reverse on output.

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

       -fg    Geographic grids (dimensions of longitude, latitude) will be  converted  to  meters
              via a “Flat Earth” approximation using the current ellipsoid parameters.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more …)
              Skip or produce header record(s). Not used with binary data.

       -icols[+l][+sscale][+ooffset][,] (more …)
              Select input columns and transformations (0 is first column).

       -r (more …)
              Set pixel node registration [gridline].

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

       -^ 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.


       For map distance unit, append unit d for arc degree, m for  arc  minute,  and  s  for  arc
       second, or e for meter [Default], f for foot, k for km, M for statute mile, n for nautical
       mile, and u for US survey foot. By default we compute such  distances  using  a  spherical
       approximation  with  great circles. Prepend - to a distance (or the unit is no distance is
       given) to perform “Flat Earth” calculations (quicker but less accurate) or  prepend  +  to
       perform exact geodesic calculations (slower but more accurate).


       To compute the u and v strain rate grids from the GPS data set gps.txt, containing x y u v
       du dv, on a 2x2 arc minute grid for California, try

              gmt gpsgridder gps.txt -R-125/-114/31/41 -I2m -fg -W -r -V


       Haines,  A.  J.  et  al.,  2015,  Enhanced  Surface  Imaging   of   Crustal   Deformation,
       SpringerBriefs in Earth Sciences, doi:10.1007/978-3-319-21578-5_2.

       Sandwell,  D.  T.  and P. Wessel, 2016, Interpolation of 2-D Vector Data Using Constraints
       from      Elasticity,      Geophys.       Res.       Lett.,       43,       10,703-10,709,


       gmt, greenspline nearneighbor, surface


       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe