Hello All


I am new to the list and am hoping to get some advice.  I am working with
statisticians who are doing the programming of a new analysis in R where we
are comparing animal tracks with environmental parameters. I was wondering
if anyone knows or has an opinion on the following:

1)      a) A rule of thumb or even a hard rule for when you need to start
using great circle instead of Euclidian calculations for distances? Just a
bit more information for perspective: depending on the animals tracked the
distances between fixes could be as small as 20 m or up to 1.5 km. The
tracks may be up to 20 km of cumulative length.

2)      b) Are functions based on Euclidian math okay to use with WGS84
coordinates if the total distance of the tracks are <20 km, or a max of 0.5
degrees of latitude (but usually much less, at latitudes of 25 or or -36
degrees). I know that with latitude the length of a degree of longitude
changes but at this scale is it a factor?  Any rules for this?

Thanks very much! I appreciate your patience and help.

Megan

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