slopeasp {landsat}

Calculate slope and aspect from elevation data.

Description

Uses gridded elevation data to calculate slope and aspect, by default using a 3x3 region. The horizontal resolution and vertical resolution must be in the same units.

Usage

slopeasp(x, EWres, NSres, EWkernel, NSkernel, smoothing=1)

Arguments

x

gridded elevation data, either as a SpatialGridDataFrame, dataframe, or matrix.

EWres

East-West grid resolution. May be omitted if x is a SpatialGridDataFrame and the horizontal units are the same as the vertical units.

NSres

North-South grid resolution. May be omitted if x is a SpatialGridDataFrame and the horizontal units are the same as the vertical units.

EWkernel

The kernel to use when calculating the East-West component of slope. If missing, a 3x3 kernel will be used.

NSkernel

The kernel to use when calculating the North-South component of slope. If missing, a 3x3 kernel will be used.

smoothing

A positive integer describing the additional smoothing to be applied, if any. smoothing=1 (default) means no smoothing will be used.

Details

By default, a 3x3 Sobel filter is used (as is standard in many GIS packages). A larger Sobel filter or a different filter will give varying results. This filter provides the third-order finite difference weighted by reciprocal of distance method proposed by Unwin (1981).

Value

slope

The slope of the DEM, in degrees

aspect

The aspect of the DEM, beginning with north and moving clockwise, and with aspect = 0 where slope = 0.

Author(s)

Sarah Goslee

References

Unwin, D. 1981. Introductory Spatial Analysis. London: Methuen. Clarke, K.C.and Lee, S.J. 2007. Spatial resolution and algorithm choice as modifiers of downslope flow computed from Digital Elevation Models. Cartography and Geographic Information Science 34:215-230.

See Also

movingwindow, topocorr

Examples

	data(dem)
	dem.slopeasp <- slopeasp(dem)

	par(mfrow=c(1,3))
	image(dem)
	image(dem.slopeasp$slope)
	image(dem.slopeasp$aspect)