rows + cols
-1) * (area of cell) less than area of flat region due to a half
row and half column missing around the perimeter.
NULL values and highly irregular
edges. The module does not [currently] attempt to correct for the
error introduced by this edge effect.
This version actually calculates area twice for each triangle pair, keeping a running minimum and maximum area depending on the direction of the diagonal used.
Reported totals are:
NULL values within the current GRASS
regionrows-1 * cols-1 *
cellarea)rows * cols *
cellarea)r.surf.area works best when the surface being evaluated extends to the edges of the current region and the cell resolution is small. Surfaces which are especially long and thin and have highly irregular boundaries will tend to have underestimated surface areas. Setting a high cell resolution (small area) will greatly reduce this impact, but will cause longer processing times.
g.region -p raster=elevation
r.surf.area map=elevation units=hectares
Null value area ignored in calculation: 0.000000
Plan area used in calculation: 20221.510000
Surface area calculation(low, high, avg):
20294.310421 20320.936368 20307.623395
Current region plan area: 20250.000000
Estimated region Surface Area: 20336.234719
NULL values by Eric
G. Miller (October 17, 2000)
Available at: r.surf.area source code (history)
Latest change: Tuesday Dec 17 20:17:20 2024 in commit: d962e90c026708a4815ea2b9f46c0e84c17de22d
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