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


       grdproject - Forward and inverse map transformation of grids


       grdproject     in_grdfile      -Gout_grdfile     -Jparameters    [     -C[dx/dy]    ]    [
       -Dxinc[unit][+e|n][/yinc[unit][*+e|n]] ] [  -Edpi ] [  -F[c|i|p|e|f|k|M|n|u] ] [  -I  ]  [
       -Mc|i|p ] [  -Rregion ] [  -V[level] ] [ -nflags ] [ -r ]

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


       grdproject  will  do  one of two things depending whether -I has been set. If set, it will
       transform a gridded data set from a rectangular  coordinate  system  onto  a  geographical
       system  by  resampling  the  surface  at  the  new  nodes.  If  not set, it will project a
       geographical gridded data set onto a rectangular grid. To obtain the  value  at  each  new
       node,  its location is inversely projected back onto the input grid after which a value is
       interpolated between the surrounding input grid values. By default bi-cubic  interpolation
       is  used.  Aliasing  is avoided by also forward projecting the input grid nodes. If two or
       more nodes are projected onto the same new  node,  their  average  will  dominate  in  the
       calculation  of  the  new node value. Interpolation and aliasing is controlled with the -n
       option. The new node spacing may be determined in one of several ways  by  specifying  the
       grid  spacing, number of nodes, or resolution. Nodes not constrained by input data are set
       to NaN.

       The -R option can be used to select a map region larger or smaller than  that  implied  by
       the extent of the grid file.


              2-D binary grid file to be transformed. (See GRID FILE FORMATS below.)

              Specify the name of the output grid file. (See GRID FILE FORMATS below.)

       -Jparameters (more ...)
              Select map projection.


              Let  projected coordinates be relative to projection center [Default is relative to
              lower left corner]. Optionally, add offsets in the projected units to be added  (or
              subtracted  when  -I  is  set)  to  (from) the projected coordinates, such as false
              eastings and northings for particular projection zones [0/0].

              Set the grid spacing for the new grid. Append m for arc minute, s for  arc  second.
              If  neither  -D  nor  -E  are set then we select the same number of output nodes as
              there are input nodes.

       -Edpi  Set the resolution for the new grid in dots per inch.

              Force 1:1 scaling, i.e., output (or input, see -I) data  are  in  actual  projected
              meters  [e].  To  specify other units, append f (foot), k (km), M (statute mile), n
              (nautical mile), u (US survey foot), i (inch), c (cm), or p  (point).  Without  -F,
              the  output  (or input, see -I) are in the units specified by PROJ_LENGTH_UNIT (but
              see -M).

       -I     Do the Inverse transformation, from rectangular to geographical.

              Append c, i, or p to indicate that cm, inch,  or  point  should  be  the  projected
              measure  unit [Default is set by PROJ_LENGTH_UNIT in gmt.conf]. Cannot be used with

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
              Specify the region of interest. You may ask to project only a subset of the grid by
              specifying  a smaller input w/e/s/n region [Default is the region given by the grid

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

       -n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more ...)
              Select interpolation mode for grids.

       -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.


       By  default  GMT  writes  out grid as single precision floats in a COARDS-complaint netCDF
       file format. However, GMT is able to produce grid files in many other commonly  used  grid
       file formats and also facilitates so called "packing" of grids, writing out floating point
       data as 1- or 2-byte integers. (more ...)


       To transform the geographical grid onto a pixel Mercator grid at 300 dpi, run

              gmt grdproject -R20/50/12/25 -Jm0.25i -E300 -r

       To inversely transform the file back onto a geographical grid, use

              gmt grdproject -R-80/-70/20/40 -Jt-75/1:500000 -I -D5m -V

       This assumes, of course, that the coordinates in were  created  with  the  same
       projection parameters.

       To  inversely  transform  the  file  (which  is  in  UTM  meters)  back  to a
       geographical grid we specify a one-to-one mapping with meter as the measure unit:

              gmt grdproject -R203/205/60/65 -Ju5/1:1 -I -Mm -V

       To inversely transform the file (which is in Mercator meters with Greenwich as the
       central  longitude and a false easting of -4 and produced on the ellipse WGS-72) back to a
       geographical grid we specify a one-to-one mapping with meter as the measure unit:

              gmt grdproject -Jm/1:1 -I -F -C-4/0 -V --PROJ_ELLIPSOID=WGS-72


       The boundaries of a projected (rectangular) data set will not necessarily give rectangular
       geographical  boundaries  (Mercator  is  one  exception). In those cases some nodes may be
       unconstrained (set to NaN).  To get a full grid back, your input grid may have to cover  a
       larger area than you are interested in.


       gmt, gmt.conf, mapproject


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