GRDVOLUME(1) Generic Mapping Tools GRDVOLUME(1)NAMEgrdvolume - Calculating volume under a surface within a contour
SYNOPSISgrdvolume grdfile [ -Ccval or -Clow/high/delta ] [ -Lbase ] [
-Rwest/east/south/north[r] ] [ -S[k] ] [ -T ] [ -V[l] ] [
-Zfact[/delta] ] [ -fcolinfo ]
DESCRIPTIONgrdvolume reads a 2-D binary grid file and calculates the volume con‐
tained 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. The contour that produced the maximum
mean height is reported as well. This feature may be used with grdfil‐
ter in designing an Optimal Robust Separator [Wessel, 1998].
grdfile
The name of the input 2-D binary grid file. (See GRID FILE FOR‐
MAT below.)
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]. The area is
measured in the plane of the contour.
-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 Carte‐
sian].
-T Use curvature minimum rather than maximum height to find best
contour value (when contour search is selected with -C).
-R xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of w/e/s/n.
The two shorthands -Rg and -Rd stand for global domain (0/360
and -180/+180 in longitude respectively, with -90/+90 in lati‐
tude). Alternatively, specify the name of an existing grid file
and the -R settings (and grid spacing, if applicable) are copied
from the grid. For calendar time coordinates you may either
give (a) relative time (relative to the selected TIME_EPOCH and
in the selected TIME_UNIT; append t to -JX|x), or (b) absolute
time of the form [date]T[clock] (append T to -JX|x). At least
one of date and clock must be present; the T is always required.
The date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
string must be of the form hh:mm:ss[.xxx]. The use of delim‐
iters and their type and positions must be exactly as indicated
(however, input, output and plot formats are customizable; see
gmtdefaults).
-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).
-f Special formatting of input and/or output columns (time or geo‐
graphical data). Specify i or o to make this apply only to
input or output [Default applies to both]. Give one or more
columns (or column ranges) separated by commas. Append T (abso‐
lute calendar time), t (relative time in chosen TIME_UNIT since
TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
to each column or column range item. Shorthand -f[i|o]g means
-f[i|o]0x,1y (geographic coordinates).
GRID FILE FORMATS
GMT is able to recognize many of the commonly used grid file formats,
as well as the precision, scale and offset of the values contained in
the grid file. When GMT needs a little help with that, you can add the
suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of
the grid type and precision, and scale and offset are optional scale
factor and offset to be applied to all grid values, and nan is the
value used to indicate missing data. See grdreformat(1) and Section
4.17 of the GMT Technical Reference and Cookbook for more information.
When reading a netCDF file that contains multiple grids, GMT will read,
by default, the first 2-dimensional grid that can find in that file. To
coax GMT into reading another multi-dimensional variable in the grid
file, append ?varname to the file name, where varname is the name of
the variable. Note that you may need to escape the special meaning of ?
in your shell program by putting a backslash in front of it, or by
placing the filename and suffix between quotes or double quotes. See
grdreformat(1) and Section 4.18 of the GMT Technical Reference and
Cookbook for more information, particularly on how to read splices of
3-, 4-, or 5-dimensional grids.
EXAMPLES
To determine the volume in km^3 under the surface hawaii_topo.grd
(height in km), use
grdvolume hawaii_topo.grd -Sk
To find the volume between the surface peaks.grd and the contour z =
250, use
grdvolume peaks.grd -Sk -C 250
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 -C 100/300/10 > results.d
To see the areas and volumes for all the contours in the previous exam‐
ple, use
grdvolume peaks.grd -Sk -Vl -C 100/300/10 > results.d
NOTESgrdvolume distinguishes between gridline and gridcell oriented grids.
In both cases the area and volume are computed up to the grid bound‐
aries. That means that in the first case the gridcells on the boundary
only contribute half their area (and volume), whereas in the second
case all gridcells are fully used. The exception is when the -C flag is
used: since contours do not extend beyond the outermost gridpoint, both
grid types are treated the same. That means the outer rim in gridcell
oriented grids is ignored when using the -C flag.
SEE ALSOGMT(1), grdfilter(1)REFERENCES
Wessel, P., 1998, An empirical method for optimal robust regional-
residual separation of geophysical data, Math. Geol., 30(4), 391-408.
GMT 4.5.14 1 Nov 2015 GRDVOLUME(1)
