Ping,

In climate analyses, we often calculate the difference in maps grid by grid (or pixel by pixel), shading the ones which are significant according to a two-tailed t test.

A sampe algorithm for performing this operation is available here: http://ccr.aos.wisc.edu/climate_modeling/modeling/data_processing/grads/grads_statsig.php. Although intented to a different software, the rationale is pretty straightforward and can be easily implemented on R.

Hope this helps,

--
Thiago V. dos Santos
PhD student
Land and Atmospheric Science
University of Minnesota
http://www.laas.umn.edu/CurrentStudents/MeettheStudents/ThiagodosSantos/index.htm
Phone: (612) 323 9898


________________________________
 From: Ping Yang <pingyang.whu@gmail.com>
To: Rainer M. Krug <Rainer@krugs.de> 
Cc: r-sig-geo <r-sig-geo@r-project.org> 
Sent: Tuesday, May 14, 2013 12:02 PM
Subject: Re: [R-sig-Geo] Raster comparrison


What I planned to do is do generate a spatial variability map of each raster and then compare them to get the difference between them. 

Or. Any comments when comparing two tasters to find out the differences and similarity between them .

Thanks,

Ping 




On May 14, 2013, at 3:57 AM, Rainer@krugs.de (Rainer M. Krug) wrote:

> Ivailo <ubuntero.9161@gmail.com> writes:
> 
>> On Mon, May 13, 2013 at 8:13 PM, ping yang <pingyang.whu@gmail.com> wrote:
>>> Dear Ivailo,
>>> 
>>> Is this method can be used to quantify the spatial variability of two
>>> raster grids? Or Is there other measurement will be better to do this?
> 
> The earth movers distance might be one option to quantify *differences*
> between maps. It is not clear to me, what you mean by "spatial
> variability of two raster maps" - do you want to determine the spatial
> variability of each raster map and then compare the two afterwards? 
> 
> Earth mover distance and e.g. mallow distance are implemented in R -
> please see precious email for links to emd implementations in R.
> 
> Cheers,
> 
> Rainer
> 
>> 
>> Dear Ping,
>> 
>> according to the author of the KappaV package (Vincent Bonhomme),
>> rasterizing the vectorial mosaics would be "neither elegant nor exact"
>> and that's why he implemented the calculation of the confusion matrix
>> (i.e. the matrix quantifying the mismatches in different regions of
>> the mosaic)  directly from the vector maps.
>> 
>>> Previously I posted a topic on how to compare two grids regarding to see
>>> the difference on spatial variabilities(e.g. two temperature grids). I am
>>> still wondering how to do it.
>> 
>> I am not aware of any R code to do such a comparison on raster
>> objects, and Cohen’s Kappa just quantifies the degree of agreement
>> between the two mosaics of interest. While writing this post I found a
>> software package at http://www.riks.nl/mck/ called the "Map Comparison
>> Kit" that might lead you further in your efforts.
>> 
>> HTH,
>> Ivailo
>> --
>> UBUNTU: a person is a person through other persons.
> 
> 
> -- 
> 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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> 
> Fax (D):    +49 - (0)3 21 21 25 22 44
> 
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> 
> Skype:      RMkrug

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