[R-sig-Geo] Raster comparrison

[Rainer M. Krug]

p m <stagis0 at gmail.com> writes:

> Dear all,
>
> I'm looking for a test to identify significant differences
> (p-value) between 2 raster maps.
>
> Can you suggest me a way to solve this problem?

Hi

Based on my understanding, you *can not* get a p value for the
difference between two entities - to ask if the two maps are
significantly different, is like asking if the two numbers 1 and two are
significantly different.

You can only answer that question if you know the underlying
distributions and can compare these.

What you can do is quantifying the difference between the two maps. One
approach I used is the Earth Movers Distance, implemented in two
packages:

http://www.rforge.net/doc/packages/emdist/emd.html 
(implemented by myself and Dirk Eddelbuettel and used in some projects) and

http://cran.r-project.org/web/packages/emdist/emdist.pdf

by Simon Urbanek (haven't used it).

But there are many other distance measures to quantify the difference
between two raster maps. Which one you choose, depends on your question.

Cheers,

Rainer

>
>
> Thank you in advance.
>
> Paul
>
> 	[[alternative HTML version deleted]]
>
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-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
Cell:       +33 - (0)6 85 62 59 98
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email:      Rainer at krugs.de

Skype:      RMkrug
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