These values are used in dem_proc()
as the default processing options:
list(
"hillshade" = c("-z", "1", "-s", "1", "-az", "315",
"-alt", "45", "-alg", "Horn",
"-combined", "-compute_edges"),
"slope" = c("-s", "1", "-alg", "Horn", "-compute_edges"),
"aspect" = c("-alg", "Horn", "-compute_edges"),
"color-relief" = character(),
"TRI" = c("-alg", "Riley", "-compute_edges"),
"TPI" = c("-compute_edges"),
"roughness" = c("-compute_edges"))
See also
https://gdal.org/programs/gdaldem.html for a description of all available command-line options for each processing mode