Hi Peter and Don,
unless you have an actual reason for only caring about the East-West axis, rather than all directions, you should include both cos and sin:
cos(exposure*PI/180) and sin(exposure*PI/180)
as Jeffrey originally suggested.
[or more generally, cos(exposure*2*PI/T) and sin(exposure*2*PI/T) where T is the period of your circular variable]

Geometrically, this maps the variable onto the unit circle (or in this case perhaps we should call it the unit compass?).
All the best
David

______________________________________________________

David Warton
Associate Professor and Australian Research Council Future Fellow
School of Mathematics and Statistics and the Evolution & Ecology Research Centre
The University of New South Wales NSW 2052 AUSTRALIA
phone (61)(2) 9385-7031
fax (61)(2) 9385-7123

http://www.eco-stats.unsw.edu.au


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