[R] correlation between two 2D point patterns?
Charles C. Berry
cberry at tajo.ucsd.edu
Sun Aug 30 17:59:55 CEST 2009
Bill,
prod( cancor( A,B )$cor )
perhaps?
Note that this accounts for linear transformations.
HTH,
Chuck
On Sun, 30 Aug 2009, William Simpson wrote:
> Suppose I have two sets of (x,y) points like this:
>
> x1<-runif(n=10)
> y1<-runif(n=10)
> A<-cbind(x1,y1)
>
> x2<-runif(n=10)
> y2<-runif(n=10)
> B<-cbind(x2,y2)
>
> I would like to measure how similar the two sets of points are.
> Something like a correlation coefficient, where 0 means the two
> patterns are unrelated, and 1 means they are identical. And in
> addition I'd like to be able to assign a p-value to the calculated
> statistic.
>
> cor(x1,x2)
> cor(y1,y2)
> gives two numbers instead of one.
>
> cor(A,B)
> gives a correlation matrix
>
> I have looked a little at spatial statistics. I have seen methods
> that, for each point, search in some neighbourhood around it and then
> compute the correlation as a function of search radius. That is not
> what I am looking for. I would like a single number that summarises
> the strength of the relationship between the two patterns.
>
> I will do procrustes on the two point sets first, so that if A is just
> a rotated, translated, scaled, reflected version of B the two patterns
> will superimpose and the statistic I'm looking for will say there is
> perfect correspondence.
>
> Thanks very much for any help in finding such a statistic and
> calculating it using R.
>
> Bill
>
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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