Provided by: gmt-common_5.4.5+dfsg-2_all bug


       sphdistance - Make Voronoi distance, node, or nearest-neighbor grid on a sphere


       sphdistance [ table ]  -Ggrdfile [  -C ] [  -Ed|n|z[dist] ] [  -Iincrement ] [  -Lunit ] [
       -Nnodetable ] [  -Qvoronoi.txt ] [  -Rregion ] [  -V[level] ] [ -bbinary ] [ -dnodata ]  [
       -eregexp ] [ -hheaders ] [ -iflags ] [ -r ] [ -:[i|o] ]

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


       sphdistance  reads one or more ASCII [or binary] files (or standard input) containing lon,
       lat and performs the construction of Voronoi polygons. These polygons are  then  processed
       to calculate the nearest distance to each node of the lattice and written to the specified
       grid.   The  Voronoi  algorithm  used  is  STRIPACK.  As  an  option,  you   may   provide
       pre-calculated  Voronoi  polygon  file  in  the  format  written  by  sphtriangulate, thus
       bypassing the memory- and time-consuming triangularization.


              Name of the output grid to hold the computed distances (but see -E for  other  node
              value options).


       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.

       -C     For large data sets you can save some memory (at the expense of more processing) by
              only storing one form of location coordinates (geographic or Cartesian 3-D vectors)
              at any given time, translating from one form to the other when  necessary  [Default
              keeps both arrays in memory]. Not applicable with -Q.

              Specify  the  quantity  that  should  be assigned to the grid nodes.  By default we
              compute distances to the nearest data point  [-Ed].   Use  -En  to  assign  the  ID
              numbers  of  the  Voronoi  polygons that each grid node is inside, or use -Ez for a
              natural nearest-neighbor grid where we assign all  nodes  inside  the  polygon  the
              z-value  of  the  center  node.   Optionally,  append the resampling interval along
              Voronoi arcs in spherical degrees [1].

              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.

       -Lunit Specify the unit used for distance calculations. Choose among d (spherical degree),
              e  (m), f (feet), k (km), M (mile), n (nautical mile) or u survey foot. A spherical
              approximation is used unless PROJ_ELLIPSOID is set to an actual ellipsoid.

              Read the information pertaining to each Voronoi polygon (the unique node  lon,  lat
              and  polygon area) from a separate file [Default acquires this information from the
              ASCII segment headers of the output file]. Required if binary input via -Q is used.

              Append the name of a file with pre-calculated Voronoi  polygons  [Default  performs
              the  Voronoi  construction on input data]. For binary data -bi you must specify the
              node information separately (via -N).

              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  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

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

       -bi[ncols][t] (more ...)
              Select native binary input. [Default is 2 input columns].

       -bo[ncols][type] (more ...)
              Select native binary output. [Default is same as input].

       -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.

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

       -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.


       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.


       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 construct Voronoi polygons from the points in the file testdata.txt and then  calculate
       distances from the data to a global 1x1 degree grid, use

              gmt sphdistance testdata.txt -Rg -I1

       To generate the same grid in two steps using sphtriangulate separately, try

              gmt sphtriangulate testdata.txt -Qv > voronoi.txt
              gmt sphdistance -Qvoronoi.txt -Rg -I1


       gmt, sphtriangulate, triangulate


       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.


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