[R-sig-Geo] Minimum bounding circle from cluster of points (Tina Cormier)

[Adrian Baddeley]

Tina Cormier <tinaacormier at gmail.com> writes:


> I have the idea now of what I need to do -

> find the longest distance between two points in the cluster,

> the midpoint of that line is the center of the circle,


Sorry, but that is not right.


The circumcircle of a set of points must pass through 3 of the points (if there are at least 3 points). The circumradius is not equal to the maximum distance between all pairs of points.


Think of an equilateral triangle: three points, each pair separated by the same distance 's'.


The circumcentre (the centre of the minimal circle) is the point at the centre of the triangle.

The circumradius is s/sqrt(3), not s/2.


Adrian


Prof Adrian Baddeley DSc FAA

Department of Mathematics and Statistics

Curtin University, Perth, Western Australia


________________________________
From: Tina Cormier <tinaacormier at gmail.com>
Sent: Monday, 11 July 2016 11:15 PM
To: Michael Sumner
Cc: chris english; Bacou, Melanie; Adrian Baddeley; r-sig-geo at r-project.org
Subject: Re: [R-sig-Geo] Minimum bounding circle from cluster of points (Tina Cormier)

Wow! I'm humbled that you all took the time to help me out! You had great suggestions and sent along some very handy functions. I have the idea now of what I need to do - find the longest distance between two points in the cluster, the midpoint of that line is the center of the circle, and there are numerous ways to create the circle, but once you have the radius, you can just buffer it. Fantastically simple. Someone also suggested using PostGIS (ST_MinimumBoundingCircle), which I will definitely try. I have a postgreSQL db that I use for some simple stuff, and I'm not a guru by any means, but this will help me gain a little more experience.

Thank you again, and I can't wait to pay if forward the next time someone asks about a topic I know well!

Cheers,
Tina


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