NAME

      grdvolume - Calculating volume under a surface within a contour

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 arguments.

      -C   find area and volume inside the cval contour.  Alternatively,
           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, grdfilter

REFERENCES

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