grdvolume(1) GMT grdvolume(1)
NAME
grdvolume - Calculate grid volume and area constrained by a contour
SYNOPSIS
grdvolume grdfile [ -Ccval or -Clow/high/delta or -Crlow/high or
-Crcval] [ -Lbase ] [ -Rregion ] [ -S[unit] ] [ -T[c|h] ] [
-V[level] ] [ -Zfact[/shift] ] [ -fflags ] [ -oflags ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
grdvolume reads a 2-D grid file and calculates the volume contained
between the surface and the plane specified by the given contour (or
zero if not given) and reports the area, volume, and maximum mean
height (volume/area). Alternatively, specify a range of contours to be
tried and grdvolume will determine the volume and area inside the con-
tour for all contour values. Using -T, the contour that produced the
maximum mean height (or maximum curvature of heights vs contour value)
is reported as well. This feature may be used with grdfilter in design-
ing an Optimal Robust Separator [Wessel, 1998].
REQUIRED ARGUMENTS
grdfile
The name of the input 2-D binary grid file. (See GRID FILE FOR-
MAT below.)
OPTIONAL ARGUMENTS
-Ccval or -Clow/high/delta or -Crlow/high or -Crcval
find area, volume and mean height (volume/area) inside the cval
contour. Alternatively, search using all contours from low to
high in steps of delta. [Default returns area, volume and mean
height of the entire grid]. The area is measured in the plane of
the contour. The Cr form on the other hand computes the volume
between the grid surface and the plans defined by low and high,
or below cval and gridas minimum. Note that this is an outside
volume whilst the other forms compute an inside (below the sur-
face) area volume. Use this form to compute for example the vol-
ume of water between two contours.
-Lbase Also add in the volume from the level of the contour down to
base [Default base is contour].
-S[unit]
For geographical grids, append a unit from e|f|k|M|n|u [Default
is meter (e)].
-T[c|h]
Determine the single contour that maximized the average height
(= volume/area). Select -Tc to use the maximum curvature of
heights versus contour value rather than the contour with the
maximum height to pick the best contour value (requires -C).
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
Specify the region of interest.
-V[level] (more a|)
Select verbosity level [c].
-Zfact[/shift]
Optionally subtract shift before scaling data by fact. [Default
is no scaling]. (Numbers in -C, -L refer to values after this
scaling has occurred).
-f[i|o]colinfo (more a|)
Specify data types of input and/or output columns.
-ocols[,a|] (more a|)
Select output columns (0 is first column).
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion of any module-specific option (but not the GMT common
options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation
of all options, then exits.
GRID FILE FORMATS
By default GMT writes out grid as single precision floats in a
COARDS-complaint netCDF file format. However, GMT is able to produce
grid files in many other commonly used grid file formats and also
facilitates so called apackinga of grids, writing out floating point
data as 1- or 2-byte integers. (more a|)
EXAMPLES
To determine the volume in km^3 under the surface hawaii_topo.nc
(height in km), use
gmt grdvolume hawaii_topo.nc -Sk
To find the volume between the surface peaks.nc and the contour z = 250
m in meters, use
gmt grdvolume peaks.nc -Se -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.nc,
use
gmt grdvolume peaks.nc -C0/300/10 -Th > results.d
To see the areas and volumes for all the contours in the previous exam-
ple, use
gmt grdvolume peaks.nc -C100/300/10 > results.d
To find the volume of water in a lake with its free surface at 0 and
max depth of 300 meters, use
gmt grdvolume lake.nc -Cr-300/0
NOTES
1. For geographical grids we convert degrees to aFlat Eartha distances
in meter. You can use -S to select another distance unit. The area
is then reported in this unit squared while the volume is reported
in unit^2 * z_unit quantities.
2. grdvolume distinguishes between gridline and pixel-registered grids.
In both cases the area and volume are computed up to the grid bound-
aries. That means that in the first case the grid cells on the
boundary only contribute half their area (and volume), whereas in
the second case all grid cells are fully used. The exception is when
the -C flag is used: since contours do not extend beyond the outer-
most grid point, both grid types are treated the same. That means
the outer rim in pixel oriented grids is ignored when using the -C
flag.
SEE ALSO
gmt(1), grdfilter(1), grdmask(1), grdmath(1)
REFERENCES
Wessel, P., 1998, An empirical method for optimal robust
regional-residual separation of geophysical data, Math. Geol., 30(4),
391-408.
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdvolume(1)
gmt5 5.4.2 - Generated Thu Jun 29 13:40:07 CDT 2017