[postgis-users] 'Clustering' records in space and time

Dylan Beaudette debeaudette at ucdavis.edu
Thu Jul 15 12:09:54 PDT 2010


Can you give us some hints about your data?

1. how many records
2. temporal domain (i.e. 1 year?)
3. spatial domain (local, regional, continental?)

If you don't have too much data, you may be able to standardize them, and 
apply an algorithm like PAM, or CLARA (see cluster package in R).


On Thursday 15 July 2010, William Furnass wrote:
> I have a PostGIS table of records describing events therefore the
> table has a timestamp attribute.  I wish to replace 'clusters' of
> events that occur within a m-hour window and a spatial radius of n
> with single events which have the mean timestamp and central position
> of the cluster.  I understand that I can quantize my data spatially
> using the St_SnapToGrid function but using this function alone I lose
> some of the distinct events that occurred at the same point in space
> but at very different times (it's my understanding that St_SnapToGrid
> only allows one point to be stored at each node in the grid).  Also, I
> am unsure as to how I could use St_SnapToGrid in such a way so as not
> to relocate points that are unique within the aforementioned spatial
> and temporal window boundaries.
> Has anyone any suggestions as to how this can be achieved
> programmatically using SQL (rather than a graphical tool)?  Should I
> perhaps be looking to use R to spatially and temporally cluster my
> data?  Apologies if the description of my problem isn't particularly
> clear; it's been a long day:)
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Dylan Beaudette
Soil Resource Laboratory
University of California at Davis

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