grdvolume - Calculate grid volume and area constrained by a contour
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.
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 contour 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 designing an Optimal Robust Separator [Wessel, 1998].
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 “packing” of grids, writing out floating point data as 1- or 2-byte integers. (more ...)
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, use
gmt grdvolume peaks.nc -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.nc, use
gmt grdvolume peaks.nc -Sk -C100/300/10 -Th > results.d
To see the areas and volumes for all the contours in the previous example, use
gmt grdvolume peaks.nc -Sk -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
grdvolume distinguishes between gridline and pixel-registered grids. In both cases the area and volume are computed up to the grid boundaries. 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 outermost 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.
Wessel, P., 1998, An empirical method for optimal robust regional-residual separation of geophysical data, Math. Geol., 30(4), 391-408.