Theory, R functions & Examples
Author: David Zelený
The function uses aspect (in degrees) and returns folded aspect, i.e. the value of the aspect “folded” along selected axis (e.g. NE–SW). The formula for folded aspect (modified from McCune & Keon 2002) is:
where aspect is the measured value of aspect, and alpha is the aspect for which the folded aspects should be zero (for folding along NE-SW axis, alpha = 45°). The formula works only for values of alpha in the range 0-180°.
Example of the use on the dataset
grasslands.env (acidophilous grasslands in Třebíč region, Czech Republic). The
grasslands.env contains variables
latitude, all in degrees. Dataset represents small plots (16-25m2) located on convex outcrops in the agricultural landscape, covered by seminatural grassland vegetation.
source ('http://anadat-r.davidzeleny.net/doku.php/en:customized_functions:folded_aspect?do=export_code&codeblock=0') # reads the function definition from above grasslands.env <- read.delim ('https://raw.githubusercontent.com/zdealveindy/anadat-r/master/data/grasslands-env.txt') # loads the file # Calculat folded aspect from grasslands.env$aspect: f.aspect <- folded_aspect (aspect = grasslands.env$aspect, alpha = 45) plot (f.aspect ~ grasslands.env$aspect) # plots values of folded aspect against the original aspect