NAME

     grdvolume - Calculating volume under a surface within a con-
     tour


SYNOPSIS

     grdvolume grdfile [ -Ccval or -Clow/high/delta ] [ -Lbase  ]
     [  -Rwest/east/south/north[r] ] [ -S[k] ] [ -T ] [ -V[l] ] [
     -Zfact[/delta] ]


DESCRIPTION

     grdvolume reads a 2-D binary grd  file  and  calculates  the
     volume contained between the surface and the plane specified
     by the given contour (or zero if not given).  Alternatively,
     specify  a  range of contours to be tried and grdvolume will
     determine the volume and area inside  the  contour  for  all
     contour  values.  The contour that produced the maximum mean
     height (volume/area) is reported as well.  This feature  may
     be  used  with  grdfilter  in  designing  an  Optimal Robust
     Separator [Wessel, 1998].

     grdfile
          The name of the input 2-D binary grd file.


OPTIONS

     No space between the option flag and  the  associated  argu-
     ments.

     -C   find area and volume inside the cval contour.  Alterna-
          tively,  search  using all contours from low to high in
          steps of  delta.   [Default  returns  entire  area  and
          volume of grid].

     -L   Also add in the volume from the level  of  the  contour
          down to base [Default base is contour].

     -S   Convert degrees to meters, append k for km [Default  is
          Cartesian].

     -T   Use curvature minimum rather  than  maximum  height  to
          find   best  contour  value  (when  contour  search  is
          selected with -C).

     -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.

     -V   Selects verbose mode, which will send progress  reports
          to  stderr  [Default runs "silently"].  Append l to see
          all the results for each  contour  level  tested  (when
          contour search has been selected).

     -Z   Optionally subtract shift before scaling data by  fact.
          [Default  is  no scaling].  (Numbers in -C, -L refer to
          values after this scaling has occurred).


EXAMPLES

     To  determine  the  volume  in  km^3   under   the   surface
     hawaii_topo.grd (height in km), try

     grdvolume hawaii_topo.grd -Sk

     To find the volume between the  surface  peaks.grd  and  the
     contour z = 250, use

     grdvolume peaks.grd -Sk -C250

     To search for the contour, between 100 and 300 in  steps  of
     10,  that  maximizes the ratio of volume to surface area for
     the file peaks.grd, use

     grdvolume peaks.grd -Sk -C100/300/10 > results.d


SEE ALSO

     gmt(l), grdfilter(l)


REFERENCES

     Wessel, P., 1998, An empirical  method  for  optimal  robust
     regional-residual  separation  of  geophysical  data,  Math.
     Geol., 30(4), 391-408.