Compute surface area of a digital elevation model.
It is often said that if Wales was flattened out it would have an area bigger than England. This function computes the surface area of a grid of heights taking into account the sloping nature of the surface.
surfaceArea(m, ...) surfaceArea.matrix(m, cellx = 1, celly = 1, byCell = FALSE)
- a matrix of height values, or an object of class SpatialPixelsDataFrame or SpatialGridDataFrame.
- the size of the grid cells in the x-direction, in the same units as the height values.
- the size of the grid cells in the y-direction, in the same units as the height values.
- return single value or matrix of values
- Either a single value of the total area if byCell=FALSE, or a matrix the same shape as m of individual cell surface areas if byCell=TRUE. In this case, the sum of the returned matrix should be the same value as that which is returned if byCell=FALSE. Missing values (NA) in the input matrix are allowed. They will produce an NA in the output matrix for byCell=TRUE, and contribute zero to the total area. They also have an effect on adjacent cells - see code comments for details.
Calculating Landscape Surface Area from Digital Elevation Models, Jeff S. Jenness Wildlife Society Bulletin, Vol. 32, No. 3 (Autumn, 2004), pp. 829-839
surfaceArea(volcano) image(surfaceArea(volcano,byCell=TRUE)) data(meuse.grid) gridded(meuse.grid) = ~x+y image(surfaceArea(meuse.grid["dist"], byCell=TRUE)) surfaceArea(meuse.grid["dist"])