1r.surf.area(1)              GRASS GIS User's Manual             r.surf.area(1)
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NAME

6       r.surf.area  - Prints estimation of surface area for raster map.
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KEYWORDS

9       raster, surface, statistics, area estimation
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SYNOPSIS

12       r.surf.area
13       r.surf.area --help
14       r.surf.area   map=name    [vscale=float]     [units=string]    [--help]
15       [--verbose]  [--quiet]  [--ui]
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17   Flags:
18       --help
19           Print usage summary
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21       --verbose
22           Verbose module output
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24       --quiet
25           Quiet module output
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27       --ui
28           Force launching GUI dialog
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30   Parameters:
31       map=name [required]
32           Name of raster map
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34       vscale=float
35           Vertical scale
36           Default: 1.0
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38       units=string
39           Output units
40           Default: square map units
41           Options: miles, feet, meters, kilometers, acres, hectares
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DESCRIPTION

44       r.surf.area calculates area of regular 3D triangulated points  (centers
45       of  cells)  in current region by adding areas of triangles.  Therefore,
46       area of a flat surface will be reported as (rows + cols -1) * (area  of
47       cell)  less  than area of flat region due to a half row and half column
48       missing around the perimeter.
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NOTES

51       This calculation is heavily dependent on data resolution (think  of  it
52       as  a  fractal  shoreline problem, the more resolution the more detail,
53       the more area, etc). This module uses the current region settings,  not
54       the resolution of the raster map. This is especially important for sur‐
55       faces with NULL values and highly irregular edges. The module does  not
56       [currently]  attempt  to  correct for the error introduced by this edge
57       effect.
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59       This version actually calculates area twice  for  each  triangle  pair,
60       keeping  a  running minimum and maximum area depending on the direction
61       of the diagonal used.
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63       Reported totals are:
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65       1      "Plan" area of NULL values within the current GRASS region
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67       2      "Plan" area within calculation region (rows-1 *  cols-1  *  cel‐
68              larea)
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70       3      Average  of  the minimum and maximum calculated 3d triangle area
71              within this region
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73       4      "Plan" area within current computational region (rows *  cols  *
74              cellarea)
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76       5      Scaling of calculated area to current region
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78       r.surf.area  works best when the surface being evaluated extends to the
79       edges of the current region and the cell resolution is small.  Surfaces
80       which are especially long and thin and have highly irregular boundaries
81       will tend to have underestimated surface areas.  Setting  a  high  cell
82       resolution (small area) will greatly reduce this impact, but will cause
83       longer processing times.
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EXAMPLES

86       g.region -p raster=elevation
87       r.surf.area map=elevation units=hectares
88       Null value area ignored in calculation: 0.000000
89       Plan area used in calculation: 20221.510000
90       Surface area calculation(low, high, avg):
91               20294.310421 20320.936368 20307.623395
92       Current region plan area: 20250.000000
93       Estimated region Surface Area: 20336.234719
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SEE ALSO

96         g.region,   r.surf.idw,   r.surf.fractal,   r.surf.gauss,   r.volume,
97       r.slope.aspect, v.to.rast
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AUTHOR

100       Bill Brown, USACERL December 21, 1994
101       Modified  for  floating point rasters and NULL values by Eric G. Miller
102       (October 17, 2000)
103       Updated for GRASS 7, and units option by Martin Landa, Czech  Technical
104       University in Prague, Czech Republic (October 2011)
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SOURCE CODE

107       Available at: r.surf.area source code (history)
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109       Accessed: Saturday Jan 21 21:15:16 2023
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111       Main  index  | Raster index | Topics index | Keywords index | Graphical
112       index | Full index
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114       © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
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118GRASS 8.2.1                                                     r.surf.area(1)
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