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grdvolume

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) 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 contour for all contour values. The contour that produced the maximum mean height 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]. The area is measured in the plane of the countour.

-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

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 wesn. The two shorthands -Rg and -Rd stand for global domain (0/360 or -180/+180 in longitude respectively, with -90/+90 in latitude). For calendar time coordinates you may either give relative time (relative to the selected TIME_EPOCH and in the selected TIME_UNIT; append t to -JX|x), or 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 delimiters and their type and positions must be as indicated (however, input/output and plotting formats are flexible).

-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), 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 -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

To see the areas and volumes for all the contours in the previous example, use

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

NOTES

grdvolume distinguishes between gridline and gridcell oriented grids. In both cases the area and volume are computed up to the grid boundaries. 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 ALSO

GMT(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.