This tool creates a new raster in which each grid cell is assigned the terrain aspect relative to a user-specified direction (`azimuth`). Relative terrain aspect is the angular distance (measured in degrees) between the land-surface aspect and the assumed regional wind azimuth (Bohner and Antonic, 2007). It is bound between 0-degrees (windward direction) and 180-degrees (leeward direction). Relative terrain aspect is the simplest of the measures of topographic exposure to wind, taking into account terrain orientation only and neglecting the influences of topographic shadowing by distant landforms and the deflection of wind by topography.

The user must input a digital elevation model (DEM) (`dem`) and an azimuth (i.e. a wind direction). The Z Conversion Factor (`zfactor`) is only important when the vertical and horizontal units are not the same in the DEM, and the DEM is in a projected coordinate system. When this is the case, the algorithm will multiply each elevation in the DEM by the Z Conversion Factor.

## Reference

Böhner, J., and Antonić, O. (2009). Land-surface parameters specific to topo-climatology. Developments in Soil Science, 33, 195-226.

## See Also

aspect

## Function Signature

`def relative_aspect(self, dem: Raster, azimuth: float = 0.0, z_factor: float = 1.0) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW