Ubuntu Manpage: grdvolume - Calculate grid volume and area constrained by a contour

Provided by: gmt-common_5.2.1+dfsg-3build1_all

NAME

       grdvolume - Calculate grid volume and area constrained by a contour

SYNOPSIS

       grdvolume grdfile [ cval or low/high/delta or rlow/high ] [ base ] [ region ] [ [unit] ] [
       [c|h] ] [ [level] ] [ fact[/shift] ] [ -f<flags> ] [ -o<flags> ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       grdvolume reads a 2-D binary 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].

REQUIRED ARGUMENTS

       grdfile
              The name of the input 2-D binary grid file. (See GRID FILE FORMAT below.)

OPTIONAL ARGUMENTS

       -Ccval or -Clow/high/delta or -Crlow/high
              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
              volume between the grid surface and the plans defined by low and  high.  Note  that
              this  is  an  outside  volume  whilst  the other forms compute an inside (below the
              surface) area volume. Use this form to compute for  example  the  volume  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]
              Convert degrees to Flat Earth distances, append a unit from e|f|k|M|n|u [Default is
              Cartesian].

       -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).

       -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
              Specify the region of interest.

       -V[level] (more ...)
              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 ...)
              Specify data types of input and/or output columns.

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              use just -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  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  options,  then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

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 "packing" of grids, writing out floating point
data as 1- or 2-byte integers. To specify the precision, scale and offset, the user should
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. In case
the two characters id is not provided, as in =/scale than a id=nf is assumed. When
reading grids, the format is generally automatically recognized. If not, the same suffix
can be added to input grid file names. See grdconvert and Section grid-file-format 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. The ?varname suffix can also be used
for output grids to specify a variable name different from the default: "z". See
grdconvert and Sections modifiers-for-CF and grid-file-format 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.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

NOTES

       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.

REFERENCES

       Wessel, P., 1998, An empirical method for optimal robust regional-residual  separation  of
       geophysical data, Math. Geol., 30(4), 391-408.

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe