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
      simple 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 inch/degree, 1:xxxxx, or
           width in inch (upper case modifier).

           CYLINDRICAL PROJECTIONS:

           -Jclon0/lat0/scale (Cassini)
           -Jjlon0/scale (Miller)
           -Jmscale (Mercator - Greenwich and Equator as origin)
           -Jmlon0/lat0/scale (Mercator - Give meridian and standard
           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)
           -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)
           -Jllon0/lat0/lat1/lat2/scale (Lambert)

           MISCELLANEOUS PROJECTIONS:

           -Jhlon0/scale (Hammer)
           -Jilon0/scale (Sinusoidal)
           -Jklon0/scale (Eckert VI)
           -Jnlon0/scale (Robinson)
           -Jrlon0/scale (Winkel Tripel)
           -Jwlon0/scale (Mollweide)

           NON-GEOGRAPHICAL PROJECTIONS:

           -Jpscale (Linear projection for polar (theta,r) coordinates)
           -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   Force pixel registration [Default is grid registration].

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

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

      -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 [inch].

      -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 geographical
      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, gmtdefaults, mapproject