DESCRIPTION

r.volume is a tool for summing cell values within clumps and calculating volumes and centroids of patches or clumps.

r.volume generates a table containing the sum of all cells from a input raster map sorted by category on a clump raster map, and optionally generates a vector points map of the centroids for each clump. If a clump map is not specified, the current MASK is used. The MASK can be defined by r.mask. The sum is multiplied by the area of a cell to give the volume occupied by that cell. See below for an example of the output table.

NOTES

If a clump map is not given and a MASK not set, the program exits with an error message.

r.volume works in the current region and respects the current MASK.

CENTROIDS

The centroid coordinates are the same as those stored in the vector map (if one was requested by centroids parameter). They are guaranteed to fall on a cell of the appropriate category, thus they are not always the true, mathematical centroid. They will always fall at a cell center.

Attribute table linked to the vector map with centroids contains several columns:

Vector points can be converted directly to a raster map with each point a separate category using v.to.rast.

APPLICATIONS

By preprocessing the elevation raster map with r.mapcalc and using suitable masking or clump maps, very interesting applications can be done with r.volume. Such as, calculating the volume of rock in a potential quarry; calculating cut/fill volumes for roads; finding water volumes in potential reservoirs.

EXAMPLE

The following report was generated by the command (North Carolina dataset): 
# set computational region
g.region raster=elevation

# compute volume
r.volume input=elevation clump=geology_30m

Volume report on data from <elevation> using clumps on <geology_30m> raster map

Category   Average   Data   # Cells        Centroid             Total
Number     in clump  Total  in clump   Easting     Northing     Volume
-----------------------------------------------------------------------------
     217    118.93  86288828  725562   635325.00   221535.00    8628882798.63
     262    108.97  21650560  198684   638935.00   222495.00    2165056037.02
     270     92.23  63578874  689373   642405.00   221485.00    6357887443.53
     405    132.96  33732662  253710   631835.00   224095.00    3373266208.59
     583    139.35   3011288   21609   630205.00   224665.00     301128821.55
     720    124.30    599618    4824   634075.00   227995.00      59961816.06
     766    132.43    936791    7074   631425.00   227845.00      93679120.08
     862    118.31   7302317   61722   630505.00   218885.00     730231746.74
     910     94.20   4235816   44964   639215.00   216365.00     423581613.11
     921    135.22   1693985   12528   630755.00   215445.00     169398523.05
     945    127.24      1145       9   630015.00   215015.00        114512.03
     946     89.91    365748    4068   639085.00   215255.00      36574833.85
     948    129.02    112632     873   630185.00   215115.00      11263181.57
-----------------------------------------------------------------------------
                                                Total Volume = 22351026655.81
The Data Total column is the sum of the elevations for each in each of the fields. The Total Volume is the sum multiplied by the east-west resolution times the north-south resolution. Note that the units on the volume may be difficult if the units of cell values on the input raster map and the resolution units differ.

SEE ALSO

r.clump, r.mask, r.mapcalc

AUTHORS

Dr. James Hinthorne, Central Washington University GIS Laboratory, December 1988.
Updated to GRASS 7 by Martin Landa, Czech Technical University in Prague, Czech Republic

Last changed: $Date$