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List:       postgis-users
Subject:    [postgis-users] Clustering adjacent points into polygons
From:       Bryan Montgomery <monty () english ! net>
Date:       2012-12-18 19:34:49
Message-ID: CAPTJ3=d1Lr+MznWCVOdMCt5twi5rKhJUnDvxw3bJf9SGcL4BJw () mail ! gmail ! com
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Hello,
So we=92ve been collecting gps data for months including the signal
strength of the cell signal. We=92ve assigned this a strength value of 1
through 5 and null. These are about 19 millions of points that we have
recorded. I=92d like to clump points within 250 feet of each other in to
one polygon.

I used the links below and tried that on a pretty small number and it
took it=92s time but it worked, assigning a group to the points with the
same strength that were within the distance of another point. From
that I was able to make a polygon that covered all the points in the
same group. http://postgis.17.n6.nabble.com/Determining-clusters-of-points-=
tt3533366.html#a3533387
 or
http://answerpot.com/showthread.php?2021386-Determining+clusters+of+points.

However, running this against the whole table of points it is taking
forever, well days and still running.

I recently came across the new indexing with Postgis 2
(http://blog.opengeo.org/2011/09/28/indexed-nearest-neighbour-search-in-pos=
tgis/)
and thought that this might help with this task.

I also was wondering if it would make sense to create 5 sub-tables of
points, one for each signal strength? I'm not sure how well the btree
and gist indexes play together?

Could I do something like taking each point, then run a query for
points ordered by distance away from the point in the question and
then keep processing rows in a function until the distance exceeds the
threshold and then move on to the next point?

Thanks,
Bryan.
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