[R-sig-Geo] calculating area

[Roger Bivand]

On Fri, 26 Jan 2007, Pedro S. A. Wolf wrote:

>  I am a psychology student who has been using R to analyze experimental data
> mainly within the general linear model for about 2 years.  I have some
> working knowledge with R, but by no means would call myself proficient so
> bear with me.  Currently I'm running a series of experiments dealing with
> spatial data.  I'm tracking peoples movements using gps units which give me
> latitude, heading, longitude, speed, altitude, and time variables.  I have
> been using the packages "maps" and "mapproj" to plot the routes which these
> individuals take which is a great visualization tool.  I would like to know
> if there is a package or set of commands which would calculate the area
> these people occupy?  So far the closest I have been able to get to
> accomplishing this task is basically taking the max and min for both lat and
> long coordinates and calculating the size of that area, but I would like
> something more accurate.  Another thing I'm trying to accomplish is creating
> what I would call a density map. This is probably not the correct term so
> let me explain what I mean.  I'm trying to characterize how people occupy
> space.  Especially how people visit certain places more than others.  Is
> there a way to create a map which shows the amount of times a particular
> place is visited by these people both within subjects and a second map
> between subjects? Help would be greatly appreciated, as my academic advisors
> know next to nothing about working with this type of data.

If you think of including humans as animals, you'll find that field
scientists, for example ecologists, do this a good deal - see the package
adehabitat, perhaps function NNCH.area for Home Range Area. The package
trip also provides tools for handling spurious GPS reports. You may find 
that you need to transform the GPS coordinates from geographical to 
projected to make area calculation easier, and that maps and mapproj will 
limit what you can do, perhaps consider moving to sp, maptools and rgdal.

(There will be an R spatial workshop at the Association of American 
Geographers conference in San Francisco on Tuesday 17 April; the "tape" of 
Edzer Pebesma's eSeminar on R spatial classes and methods is not yet 
online, but we'll post when it is ready:

http://www.wun.ac.uk/ggisa/seminars/archive/2006_program/index.html

is where it should turn up).

Roger

> 
> Pedro
> 
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> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no