If you want a measure of exposure, i. e., heat, I suggest using the
heatload transformation suggested by McCune and Grace (2002). Their
assumption is that mid-afternoon, when the sun is in the southwest, is
usually the warmest time of day. The formula at the end of Chapter 3
follows:
heat load index=(1-cos(degrees-45))/2
McCune, Bruce and James B. Grace. 2002. Analysis of ecological
communities. MJM Software Design. Gleneden Beach, Oregon. USA
Mike Marsh
On 10/16/2013 3:00 AM, r-sig-ecology-requ...@r-project.org wrote:
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Today's Topics:
1. angular statistics (Peter Nelson)
2. Re: angular statistics (Holland, Jeffrey D)
3. Re: angular statistics (Don McKenzie)
4. Re: angular statistics (Peter Nelson)
5. Re: angular statistics (Donald McKenzie)
--
Message: 1
Date: Tue, 15 Oct 2013 09:59:38 -0700
From: Peter Nelson pnel...@cfr-west.org
To: r-sig-ecology@r-project.org
Subject: [R-sig-eco] angular statistics
Message-ID: 0c3c26ea-5599-4570-b205-5feecb70b...@cfr-west.org
Content-Type: text/plain; charset=us-ascii
I want to include the exposure (measured in degrees, for example, East-facing
is 90) of various coastal sites in GLM and CCA analyses. Is there an
appropriate transformation that I can apply to these measurements that will
allow me to do this? I've found plenty of information on comparing headings,
calculating means, etc, but nothing on how exposure might be used as a
continuous independent variable.
Treating exposure as a categorical variable (East, Southwest, etc) seems like a
fallback option, but then there is just as much of a 'difference' between SE
and E sites as there is between SE and NW sites!
Thanks, Pete
--
Message: 2
Date: Tue, 15 Oct 2013 17:10:43 +
From: Holland, Jeffrey D jdhol...@purdue.edu
To: R-sig-ecology@r-project.org R-sig-ecology@r-project.org
Subject: Re: [R-sig-eco] angular statistics
Message-ID:
30a9cce0a986f74c837d6f87f9c581861367e...@wpvexcmbx01.purdue.lcl
Content-Type: text/plain; charset=us-ascii
Hello Pete,
You could include the sine and cosine of the angles. A good book on this
kind of analysis:
Fisher, N.I. 1993. Statistical Analysis of Circular Data. Cambridge Univ. Press.
To make this closer to exposure, perhaps you could first rotate the compass
so that 360' is facing the direction of maximum exposure, and back-transform later? Just
a thought.
Cheers, Jeff
Jeffrey D. Holland (765) 494-7739
Assoc. Prof. of Landscape Ecology Biodiversityjdhollan #at# purdue.edu
Dept. of Entomology, Purdue University Smith Hall B17, 901 W.
State St., West Lafayette, IN 47907
-Original Message-
From: r-sig-ecology-boun...@r-project.org
[mailto:r-sig-ecology-boun...@r-project.org] On Behalf Of Peter Nelson
Sent: Tuesday, October 15, 2013 1:00 PM
To: r-sig-ecology@r-project.org
Subject: [R-sig-eco] angular statistics
I want to include the exposure (measured in degrees, for example, East-facing
is 90) of various coastal sites in GLM and CCA analyses. Is there an
appropriate transformation that I can apply to these measurements that will
allow me to do this? I've found plenty of information on comparing headings,
calculating means, etc, but nothing on how exposure might be used as a
continuous independent variable.
Treating exposure as a categorical variable (East, Southwest, etc) seems like a
fallback option, but then there is just as much of a 'difference' between SE
and E sites as there is between SE and NW sites!
Thanks, Pete
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Message: 3
Date: Tue, 15 Oct 2013 11:45:14 -0700
From: Don McKenzie d...@u.washington.edu
To: Peter Nelson pnel...@cfr-west.org
Cc: r-sig-ecology@r-project.org
Subject: Re: [R-sig-eco] angular statistics
Message-ID: cd8bb4be-0db6-4863-b8af-1d7443d79...@u.washington.edu
Content-Type: text/plain
There is precedent in the ecological literature for using a cosine transformation IF you have
reason to believe that your predictor varies continuously and symmetrically in its effects around a
circle. For example, if due east were the most exposure, and due west the least, with
due north and south being roughly equal, you could
