[R-sig-eco] spatstat: help with calculating number of clusters, cluster size

[Marcelino de la Cruz]

Hi Soumya,

There are several ways. If you are certain that 
your trees are clustered,  you could consider as 
a first option fitting Poisson cluster or 
Thomas  processes by minimum contrast methods. In 
spatstat you can do this, for example, with function thomas.estK .
 From the fitted parameters you will obtain both 
kappa (the intensity of "parent" points , i.e. an 
approximation to the "number" of clusters) and 
sigma (the standard deviation of the distribution 
of "offspring" points around the parents, so you 
could approximate the radius as 2*sigma).

You can also use  the spatstat-based package 
ecespa 
(http://cran.r-project.org/web/packages/ecespa/index.html); 
see the help pages of  the functions pc.estK  and 
ipc.estK  for complete examples of fitting 
homogeneous and inhomogeneous processes.

Cheers,

Marcelino



At 12:49 13/06/2009, Soumya Prasad wrote:
>Hi,
>
>I am new to spatial statistics and have a few basic queries. I am
>analysing the spatial pattern of trees on a large plot. I wanted to
>know if there is there some way of obtaining estimates of the number
>of clusters and cluster-radius (in an iterative fashion) after fitting
>a spatial point process to observed data (through 'ppm')?
>
>Thanks in advance,
>Soumya
>
>--
>
>Soumya Prasad
>Centre for Ecological Sciences
>Indian Institute of Science
>Bangalore 560012
>India
>
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>R-sig-ecology at r-project.org
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________________________________

Marcelino de la Cruz Rot

Departamento de  Biología Vegetal
E.U.T.I. Agrícola
Universidad Politécnica de Madrid
28040-Madrid
Tel.: 91 336 54 35
Fax: 91 336 56 56
marcelino.delacruz at upm.es
_________________________________