debian man page for grdtrack

GRDTRACK(l)															       GRDTRACK(l)

NAME
       grdtrack - Sampling of a 2-D grdfile along 1-D trackline (a sequence of x,y points)

SYNOPSIS
       grdtrack xyfile -Ggrdfile [ -H[nrec] ] [ -L[flag] ] [ -M[flag] ] [ -Q ] [ -Rwest/east/south/north ] [ -S ] [ -V ] [ -Z ] [ -: ] [ -bi[s][n]
       ] [ -bo[s][n] ]

DESCRIPTION
       grdtrack reads a grdfile and a table (from file or standard input) with (x,y) positions in the first  two  columns  (more  columns  may	be
       present).  It interpolates the grid at the positions in the table and writes out the table with the interpolated values added as a new col-
       umn. A bicubic [Default] or bilinear [-Q] interpolation is used, requiring boundary conditions at the limits  of  the  region  (see  -Lflag
       option).

       xyfile This  is an ASCII [or binary, see -b] file where the first 2 columns hold the (x,y) positions where the user wants to sample the 2-D
	      data set.

       -G     grdfile is a 2-D binary grd file with the function f(x,y).

OPTIONS
       No space between the option flag and the associated arguments.

       -H     Input file(s) has Header record(s). Number of header records can be changed by editing your .gmtdefaults file. If used, GMT  default
	      is 1 header record.

       -L     Boundary condition flag may be x or y or xy indicating data is periodic in range of x or y or both set by -R, or flag may be g indi-
	      cating geographical conditions (x and y are lon and lat). [Default uses "natural" conditions (second partial  derivative	normal	to
	      edge is zero).]  If no flag is supplied, it is assumed that the x column contains longitudes, which may differ from the region in -R
	      by [multiples of] 360 degrees [Default assumes no periodicity].

       -M     Multiple segment file. Segment separator is a record beginning with flag.  [Default is '>'].

       -Q     Quick mode. Use bilinear rather than bicubic interpolation.

       -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.

       -S     Suppress the output of interpolated points that result in NaN values.

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

       -Z     Only write out the sampled z-values [Default writes all columns].

       -:     Toggles between (lon,lat) and (lat,lon) input/output. [Default is (lon,lat)]

       -bi    Selects  binary input. Append s for single precision [Default is double].  Append n for the number of columns in the binary file(s).
	      [Default is 2 input columns].

       -bo    Selects binary output. Append s for single precision [Default is double].

HINTS
       If an interpolation point is not on a node of the input grid, then a NaN at any node in the neighborhood surrounding the point  will  yield
       an interpolated NaN. Bicubic interpolation [default] yields continuous first derivatives but requires a neighborhood of 4 nodes by 4 nodes.
       Bilinear interpolation [-Q] uses only a 2 by 2 neighborhood, but yields only zeroth-order continuity. Use bicubic when smoothness is impor-
       tant. Use bilinear to minimize the propagation of NaNs.

EXAMPLES
       To  sample  the	file hawaii_topo.grd along the SEASAT track track_4.xyg (An ASCII table containing longitude, latitude, and SEASAT-derived
       gravity, preceeded by one header record), try

       grdtrack track_4.xyg -Ghawaii_topo.grd -H > track_4.xygt

SEE ALSO
       gmt(1gmt), surface(1gmt), sample1d(1gmt)

								    1 Jan 2004							       GRDTRACK(l)