Ubuntu Manpage: grdproject - Forward and inverse map transformation of grids

Provided by: gmt-common_5.2.1+dfsg-3build1_all

NAME

       grdproject - Forward and inverse map transformation of grids

SYNOPSIS

       grdproject      in_grdfile      out_grdfile      parameters      [     [dx/dy]     ]     [
       xinc[unit][=|+][/yinc[unit][=|+]] ] [ dpi ] [ [c|i|p|e|f|k|M|n|u] ]  [   ]  [  c|i|p  ]  [
       region ] [ [level] ] [ -n<flags> ] [ -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  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.

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 ...)
              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 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].

       -Dxinc[unit][=|+][/yinc[unit][=|+]]
              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 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.

       -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.

       -R[unit]xmin/xmax/ymin/ymax[r] (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
              file].

       -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
              use just -).

       -+ 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  options,  then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

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 "packing" of grids, writing out floating point
data as 1- or 2-byte integers. To specify the precision, scale and offset, the user should
add the suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of the grid
type and precision, and scale and offset are optional scale factor and offset to be
applied to all grid values, and nan is the value used to indicate missing data. In case
the two characters id is not provided, as in =/scale than a id=nf is assumed. When
reading grids, the format is generally automatically recognized. If not, the same suffix
can be added to input grid file names. See grdconvert and Section grid-file-format of the
GMT Technical Reference and Cookbook for more information.

When reading a netCDF file that contains multiple grids, GMT will read, by default, the
first 2-dimensional grid that can find in that file. To coax GMT into reading another
multi-dimensional variable in the grid file, append ?varname to the file name, where
varname is the name of the variable. Note that you may need to escape the special meaning
of ? in your shell program by putting a backslash in front of it, or by placing the
filename and suffix between quotes or double quotes. The ?varname suffix can also be used
for output grids to specify a variable name different from the default: "z". See
grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical
Reference and Cookbook for more information, particularly on how to read splices of 3-,
4-, or 5-dimensional grids.

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  created  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 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.

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe