[GRASSLIST:5242] Re: Local density analysis script for GRASS 5.7

[Benjamin Ducke]

Sounds interesting. I have some site maps here that I would like
to test it on.
Could you give me some lit reference for Ian Johnson's LDA algorithm?

Cheers,

Benjamin

On Sun, 02 Jan 2005 18:31:28 -0700
Michael Barton <michael.barton at asu.edu> wrote:

> Here is something I've wanted to do for awhile.
> 
> This script calculates Ian Johnson's Local Density Analysis for vector
> points. It is used in archaeology to examine the degree of clustering at
> varying neighborhood radii of sites or artifacts or the degree of clustering
> of one artifact class in the vicinity of another artifact class. It is a
> nice routine, but rarely available.
> 
> I've been futzing with this for awhile in GRASS and finally worked out how
> to do it. The problem was determining the number of points within a given
> radius of a point. This should not be difficult in a GIS like GRASS, but it
> is surprisingly tricky. R.neighbors doesn't have a count option and hacking
> it by giving all relevant cells a cat of one and doing a sum doesn't give a
> correct answer. Buffering also doesn't give the same answer as summing the
> count of point around each point as the latter can count some points twice
> (correctly), whereas buffering only will count them once. V.neighbors
> produces an output that is NOT a count of points around each point but
> something quite different. Anyway, I was able to use v.distance with the -a
> and -p flags to get this. This method may be useful for other kinds of
> similar clustering or neighborhood analyses.
> 
> For simply looking at the degree of clustering in a points file, use the
> same file for the base and analysis files. For looking at the degree of
> clustering for points of type 2 in the neighborhood of points of type 1, use
> type 1 for the base file and type 2 for the analysis file.
> 
> You can select minimum and maximum neighborhood radii, along with a value to
> increment the neighborhood radius from minimum to maximum.
> 
> The main output is in a text file, to which you can append a series of
> analyses. For a single analysis, you can also have a line graph of the
> results displayed. 
> 
> I've used this kind LDA with an algorithm described by Ian Johnson for
> MapInfo and in Keith Kintigh's archaeological analysis program. The results
> look correct here. But I'd appreciate it if anyone cares to test it and let
> me know what they think.
> 
> I'll post this on my website in the script exchange area.
> 
> Cheers and Happy New Year
> Michael Barton
> ____________________
> C. Michael Barton, Professor of Anthropology
> School of Human Evolution and Social Change
> PO Box 872402
> Arizona State University
> Tempe, AZ  85287-2402
> USA
> 
> Phone: 480-965-6262
> Fax: 480-965-7671
> www: <www.public.asu.edu/~cmbarton>
> 
>