NAME

     grdproject - Forward and Inverse map transformation  of  2-D
     grd files


SYNOPSIS

     grdproject              in_grdfile              -Jparameters
     -Rwest/east/south/north[r] [ -Ddx[m|c][/dy[m|c]] ] [ -Edpi ]
     [ -F ] [ -Gout_grdfile ] [ -I ] [ -M[m]  ]  [  -Nnx/ny  ]  [
     -Ssearch_radius ] [ -V ]


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.  The new nodes are filled based on a sim-
     ple weighted average of nearby points.  Aliasing is  avoided
     by  using  sensible  values  for the search_radius.  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.
          No space between the option  flag  and  the  associated
     arguments.   Use  upper  case for the option flags and lower
     case for modifiers.

     in_grdfile
          2-D binary grd file to be transformed.

     -J   Selects  the  map  projection.  Scale  is  UNIT/degree,
          1:xxxxx,  or width in UNIT (upper case modifier).  UNIT
          is cm, inch, or m, depending on the  MEASURE_UNIT  set-
          ting in .gmtdefaults, but this can be overridden on the
          command line by  appending  the  c,  i,  or  m  to  the
          scale/width value.

          CYLINDRICAL PROJECTIONS:

          -Jclon0/lat0/scale (Cassini)
          -Jjlon0/scale (Miller)
          -Jmscale (Mercator - Greenwich and Equator as origin)
          -Jmlon0/lat0/scale (Mercator - Give meridian and  stan-
          dard parallel)
          -Joalon0/lat0/azimuth/scale (Oblique Mercator  -  point
          and azimuth)
          -Joblon0/lat0/lon1/lat1/scale (Oblique Mercator  -  two
          points)
          -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point
          and pole)
          -Jqlon0/scale   (Equidistant   Cylindrical   Projection
          (Plate Carree))
          -Jtlon0/scale (TM - Transverse Mercator,  with  Equator
          as y = 0)
          -Jtlon0/lat0/scale (TM - Transverse Mercator, set  ori-
          gin)
          -Juzone/scale (UTM - Universal Transverse Mercator)
          -Jylon0/lats/scale (Basic Cylindrical Projection)

          AZIMUTHAL PROJECTIONS:

          -Jalon0/lat0/scale (Lambert).
          -Jelon0/lat0/scale (Equidistant).
          -Jflon0/lat0/horizon/scale (Gnomonic).
          -Jglon0/lat0/scale (Orthographic).
          -Jslon0/lat0/scale (General Stereographic)

          CONIC PROJECTIONS:

          -Jblon0/lat0/lat1/lat2/scale (Albers)
          -Jdlon0/lat0/lat1/lat2/scale (Equidistant)
          -Jllon0/lat0/lat1/lat2/scale (Lambert)

          MISCELLANEOUS PROJECTIONS:

          -Jhlon0/scale (Hammer)
          -Jilon0/scale (Sinusoidal)
          -Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
          -Jnlon0/scale (Robinson)
          -Jrlon0/scale (Winkel Tripel)
          -Jvlon0/scale (Van der Grinten)
          -Jwlon0/scale (Mollweide)

          NON-GEOGRAPHICAL PROJECTIONS:

          -Jpscale[/origin] (polar (theta,r) coordinates, option-
          ally offset theta [0])
          -Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log,  and
          power scaling)
          More details can be found in the psbasemap manpages.

     -R   west, east, south, and  north  specify  the  Region  of
          interest.  To specify boundaries in degrees and minutes
          [and seconds], use the dd:mm[:ss] format.  Append r  if
          lower  left  and  upper right map coordinates are given
          instead of wesn.


OPTIONS

     -D   Set the grid spacing for the new grid.   Append  m  for
          minutes, c for seconds.

     -E   Set the resolution for the new grid in dots pr inch.

     -F   Toggle between pixel and gridline registration [Default
          is same as input].

     -G   Specify the name of the output netCDF grd file.

     -I   Do the Inverse transformation, from rectangular to geo-
          graphical.

     -M   Let transformed coordinates be relative  to  projection
          center  [Default  is  relative  to  lower left corner].
          Append m to indicate that meters should be the  measure
          unit [Default is set in .gmtdefaults].

     -N   Set the number of grid nodes in the new grid.

     -S   Set the  search  radius  for  the  averaging  procedure
          [Default avoids aliasing].

     -V   Selects verbose mode, which will send progress  reports
          to stderr [Default runs "silently"].


EXAMPLES

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

     grdproject  dbdb5.grd  -R20/50/12/25   -Jm0.25i   -E300   -F
     -Gdbdb5_merc.grd

     To inversely transform the file topo_tm.grd back onto a geo-
     graphical grid try

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

     This assumes, of course, that the coordinates in topo_tm.grd
     were created with the same projection parameters.
     To inversely transform the file topo_utm.grd  (which  is  in
     UTM  meters) back onto a geographical grid we specify a one-
     to-one mapping with meter as the measure unit:

     grdproject topo_utm.grd -R203/05/60/65 -Ju5/1:1  -I  -Mm  -V
     -Gtopo.grd


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
     interrested in.


SEE ALSO

     gmt(l), gmtdefaults(l), mapproject(l)