Description Usage Arguments Details Value Author(s) References See Also Examples

Uses gridded elevation data to calculate slope and aspect, by default using a 3x3 region.

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

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

`EWres` |
East-West grid resolution. May be omitted if x is a SpatialGridDataFrame. |

`NSres` |
North-South grid resolution. May be omitted if x is a SpatialGridDataFrame. |

`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. |

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).

`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. |

Sarah Goslee

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.

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