GRASS GIS manual: r.volume

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NAME

r.volume - Calculates the volume of data "clumps", and (optionally) produces a GRASS vector points map containing the calculated centroids of these clumps.

KEYWORDS

raster, volume

SYNOPSIS

r.volume
r.volume help
r.volume [-f] data=string [clump=string] [centroids=string] [--overwrite] [--verbose] [--quiet]

Flags:

-f: Generate unformatted report
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

data=string: Existing raster map representing data that will be summed within clumps
clump=string: Existing raster map, preferably the output of r.clump
centroids=string: Vector points map to contain clump centroids

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 data_map layer sorted by category on a clump 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 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.

EXAMPLE

The following report was generated by the command: (spearfish data base; fields.only is the fields layer without the National Forest category)

r.volume data=elevation clump=fields.only centroids=field.centers


Volume report on data from elevation using clumps on fields.only map

 Cat    Average   Data   # Cells        Centroid             Total
Number  in clump  Total  in clump   Easting   Northing       Volume

    1   1181.09   75590      64   595500.00  4927700.00   755900000.00
    2   1163.50   69810      60   597100.00  4927700.00   698100000.00
    3   1146.83   34405      30   598300.00  4927700.00   344050000.00
    4   1193.20  366311     307   599400.00  4927300.00  3663110000.00
        .....
        .....   
        .....
   60   1260.08  351563     279   603100.00  4921000.00  3515630000.00
   61   1213.93   35204      29   603700.00  4921500.00   352040000.00
   62   1207.71   33816      28   604100.00  4921500.00   338160000.00
                                         Total Volume = 67226740000.00

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 e-w resolution times the n-s resolution. Note that the units on the volume may be difficult if the units of cell values on the data_map layer and the resolution units differ.

CENTROIDS

The centroid coordinates are the same as those stored in the sites file (if one was requested). 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.

FORMAT OF CENTROIDS table

For each line of above table the vector points table contains these columns: easting, northing, cat, volume, average, sum, count

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

APPLICATIONS

By preprocessing the elevation layer 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. Data layers of other measures of real values.

AUTHOR

Dr. James Hinthorne, Central Washington University GIS Laboratory
December 1988.

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