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grdproject(1)                         GMT                        grdproject(1)




NAME

       grdproject - Forward and inverse map transformation of grids


SYNOPSIS

       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.


DESCRIPTION

       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 coordi-
       nate 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 pro-
       jected onto the same new node, their average will dominate in the  cal-
       culation  of  the  new  node  value. Interpolation and aliasing is con-
       trolled 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.


REQUIRED ARGUMENTS

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

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

       -Jparameters (more a|)
              Select map projection.


OPTIONAL ARGUMENTS

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

       -Dxinc[unit][+e|n][/yinc[unit][+e|n]]
              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.

       -F[c|i|p|e|f|k|M|n|u]
              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 sur-
              vey foot), i (inch), c (cm), or p (point). Without -F, the  out-
              put   (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.

       -Mc|i|p
              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 -F.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
              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 file].

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

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

       -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.


GRID FILE FORMATS

       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 apackinga of grids, writing  out  floating  point
       data as 1- or 2-byte integers. (more a|)


EXAMPLES

       To  transform the geographical grid dbdb5.nc onto a pixel Mercator grid
       at 300 dpi, run

              gmt grdproject dbdb5.nc -R20/50/12/25 -Jm0.25i -E300 -r -Gdbdb5_merc.nc

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

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

       This  assumes,  of course, that the coordinates in topo_tm.nc were cre-
       ated with the same projection parameters.

       To inversely transform the file topo_utm.nc (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 topo_utm.nc -R203/205/60/65 -Ju5/1:1 -I -Mm -Gtopo.nc -V

       To inversely transform the file data.nc (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 data.nc -Jm/1:1 -I -F -C-4/0 -Gdata_geo.nc -V --PROJ_ELLIPSOID=WGS-72


RESTRICTIONS

       The boundaries of a projected (rectangular) data set will not necessar-
       ily give rectangular geographical boundaries (Mercator  is  one  excep-
       tion). 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.


SEE ALSO

       gmt(1), gmt.conf(5), mapproject(1)


COPYRIGHT

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



5.4.2                            Jun 24, 2017                    grdproject(1)

gmt5 5.4.2 - Generated Thu Jun 29 07:42:20 CDT 2017
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