.TH GRDVOLUME l "1 Mar 2002"
.SH NAME
grdvolume \- Calculating volume under a surface within a contour
.SH SYNOPSIS
\fBgrdvolume\fP \fIgrdfile\fP [ \fB\-C\fP\fIcval\fP or \fB\-C\fP\fIlow/high/delta\fP ]
[ \fB\-L\fP\fIbase\fP ] [ \fB\-R\fP\fIwest/east/south/north\fP[\fBr\fP] ] [ \fB\-S\fP[\fBk\fP] ] [ \fB\-T\fP ] [ \fB\-V\fP[\fBl\fP] ] [ \fB\-Z\fP\fIfact\fP[/\fIdelta\fP] ]
.SH DESCRIPTION
\fBgrdvolume\fP 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 \fBgrdvolume\fP 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
\fBgrdfilter\fP in designing an Optimal Robust Separator [\fIWessel\fP, 1998].
.TP
\fIgrdfile\fP
The name of the input 2-D binary grd file.
.SH OPTIONS
No space between the option flag and the associated arguments.
.TP
.B \-C
find area and volume inside the \fIcval\fP contour. Alternatively, search using
all contours from \fIlow\fP to \fIhigh\fP in steps of \fIdelta\fP. [Default returns
entire area and volume of grid]. The area is measured in the plane of the countour.
.TP
.B \-L
Also add in the volume from the level of the contour down to \fIbase\fP [Default base is contour].
.TP
.B \-S
Convert degrees to meters, append \fBk\fP for km [Default is Cartesian].
.TP
.B \-T
Use curvature minimum rather than maximum height to find best contour value (when contour
search is selected with \fB\-C\fP).
.TP
.B \-R
\fIwest, east, south,\fP and \fInorth\fP specify the Region of interest. To specify boundaries
in degrees and minutes [and seconds], use the dd:mm[:ss] format. Append \fBr\fP if lower left and upper right
map coordinates are given instead of wesn.
.TP
.B \-V
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
Append \fBl\fP to see all the results for each contour level tested (when contour search
has been selected).
.TP
.B \-Z
Optionally subtract \fIshift\fP before scaling data by \fIfact\fP. [Default is no scaling].
(Numbers in \fB\-C, -L\fP refer to values after this scaling has occurred).
.SH EXAMPLES
To determine the volume in km^3 under the surface hawaii_topo.grd (height in km), try
.br
.sp
grdvolume hawaii_topo.grd \fB\-Sk\fP
.br
.sp
To find the volume between the surface peaks.grd and the contour z = 250, use
.br
.sp
grdvolume peaks.grd \fB\-Sk\fP \fB\-C\fP250
.br
.sp
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
.br
.sp
grdvolume peaks.grd \fB\-Sk\fP \fB\-C\fP100/300/10 > results.d
.br
.sp
To see the areas and volumes for all the countours in the previous example, try
.br
.sp
grdvolume peaks.grd \fB\-Sk \-Vl\fP \fB\-C\fP100/300/10 > results.d
.SH "SEE ALSO"
.IR gmt (l),
.IR grdfilter (l)
.SH REFERENCES
Wessel, P., 1998, An empirical method for optimal robust regional-residual separation of geophysical data,
\fIMath. Geol., 30(4)\fP, 391\-408.