raster (version 1.8-9)

Slope and aspect: Slope and aspect

Description

Compute slope and/or aspect from elevation data. Elevation data should be in map units (typically meter for projected raster data), or in meters when the coordinate reference system (CRS) is longitude/latitude.

Usage

slopeAspect(dem, filename='', type='', unit='', neighbors=8, flatAspect, ...)

Arguments

dem

RasterLayer object with elevation values in map units, or in meters when the crs is longitude/latitude

filename

Character. Filename. optional

type

Character. 'slope', 'aspect', or 'both' (=default, slope and aspect)

unit

Character. 'degrees' or '' (=default, radians for aspect, and fraction for slope)

neighbors

Integer. Indicating how many neighboring cells to use to compute slope for any cell. Either 8 (queen case) or 4 (rook case), see Details.

flatAspect

Numeric or NA. What value to use for aspect when slope is zero (and hence the aspect is undefined)? The default value is 90 degrees (or 0.5*pi radians)

...

Standard additional arguments for writing RasterLayer files

Details

When neighbors==4, slope and aspect are computed according to Fleming and Hoffer (1979) and Ritter (1987). When neigbors==8, slope and aspect are computed according to Horn (1981). The Horn algorithm may be best for rough surfaces, and the Fleming and Hoffer algorithm may be better for smoother surfaces (Jones, 1997; Burrough and McDonnell, 1998).

References

Burrough, P., and R.A. McDonnell, 1998. Principles of Geographical Information Systems. Oxford University Press. Fleming, M.D. and Hoffer, R.M., 1979. Machine processing of landsat MSS data and DMA topographic data for forest cover type mapping. LARS Technical Report 062879. Laboratory for Applications of Remote Sensing, Purdue University, West Lafayette, Indiana. Horn, B.K.P., 1981. Hill shading and the reflectance map. Proceedings of the IEEE 69(1):14-47 Jones, K.H., 1998. A comparison of algorithms used to compute hill slope as a property of the DEM. Computers & Geosciences 24(4): 315-323 Ritter, P., 1987. A vector-based slope and aspect generation algorithm. Photogrammetric Engineering and Remote Sensing 53 (8):1109-1111

See Also

hillShade