Northerness, easterness and slope may be some of the simpler proxies for solar radiation which can be calculated by GIS.
As aspect is a circular land-surface parameter, a sine (eastness) or cosine (northness) transformation can be used to obtain a continuous gradient, stressing the north-south or east-west gradient.
In the northern hemisphere for instance, slopes facing south receive more potential insolation than those facing north; a relation between northerness and slope can also be established.
Let's do some calculations with
# build a VRT from a list of datasets
gdalbuildvrt -input_file_list dem_tiles.txt dem.vrt
# r.external - Links GDAL supported raster data as a pseudo GRASS raster map
r.external input=C:\data\dem.vrt output=dem10m
# calculation of northerness, easterness and the interaction between northerness and slope
r.northerness.easterness --verbose elevation=dem10m
The result maps of r.northerness.easterness are
- northerness: cos(aspect)
- easterness: sin(aspect)
- interaction between northerness and slope: northerness*slope
|DEM 10m x 10m|
|DEM 10m x 10m (zoomed)|
Let's do some checks in the field.