[R-sig-Geo] Minimum bounding circle from cluster of points

[Mathieu Rajerison]

There was the answer in R here :
http://www.psychologie.uni-kiel.de/de#draw-the-minimum-bounding-box

But the page doesn't seem to exist anymore..
ᐧ

2016-07-11 17:26 GMT+02:00 Tina Cormier <TinaACormier at gmail.com>:

> 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 the center point. 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
> ***********************************************************************
> In SUMMARY, functions that solve this problem are listed below:
>
> 1. Using a *3-liner* from Robert Hijmans, using optimization:
> library(raster)
> library(rgeos)
>
> set.seed(7)
> n <- 4
> xy <- cbind(runif(n), runif(n))
>
>
>
>
> *f <- function(p) { max(pointDistance(rbind(p), xy, lonlat=FALSE)) }p <-
> optim(colMeans(xy), f)cc <- buffer(SpatialPoints(rbind(p$par)),
> width=p$value, quadsegs=45)*
> plot(cc)
> points(xy, pch=20, cex=1.5)
> points(rbind(p$par), pch='*', col='red', cex=3)
> lines(rbind(p$par, c(p$par[1]+p$value, p$par[2])), col='blue', lwd=2,
> lty=2)
> text(p$par[1]+0.5*p$value, p$par[2], paste("radius =", round(p$value,
> 2)), pos=3, cex=.85)
> text(p$par[1], p$par[2], labels=paste0("(",paste(round(p$par, 2),
> collapse=", "), ")"), pos=1, cex=.75)
> ***********************************************************************
>
> 2. A function from Adrian Baddeley using spatstat
> library(spatstat)
>
> circumcircle <- function(x, ...) {   UseMethod("circumcircle") }
>
> circumcircle.owin <- function(x, ...) {
>   d2 <- fardist(x, ..., squared=TRUE)
>   z <- where.min(d2)
>   r <- sqrt(min(d2))
>   w <- disc(centre=z, radius=r)
>   return(w)
> }
>
> circumcircle.ppp <- function(x, ...) {
>   circumcircle(convexhull(x))
> }
> ***********************************************************************
>
> 3. A handy link that walks through the process in a bit longer way around,
> but still works:
> http://www.uni-kiel.de/psychologie/rexrepos/posts/diagBounding.html
>
>
> On Fri, Jul 8, 2016 at 10:31 AM, Tina Cormier <TinaACormier at gmail.com>
> wrote:
>
> > Hi all,
> >
> > Looking for help aggregating some field data subplots to the plot level
> > (data currently in shapefile format). I have clusters of 4 points (4
> > subplots = 1 plot). I'd like to create a circle around each cluster that
> is
> > the smallest circle that would encompass all 4 points. Sort of like a
> > convex hull, but a circle (convex hull, in this case, would give me a
> > triangle because of the layout of the subplots). I am familiar with (and
> > use frequently) the typical geo packages in R - with rgdal, sp, raster,
> and
> > maptools being my most frequent flyers. Is there a function I'm missing
> in
> > these (or some other) packages that might be able to help me out? In the
> > attribute table, I have a unique ID for each plot/cluster. So for each
> plot
> > ID (in this case, consisting of 4 subplots), I'd like to build a circle
> > around all of the subplots.
> >
> > > str(pts)
> > Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
> >   ..@ data       :'data.frame': 160 obs. of  12 variables:
> >   .. ..$ Plot      : num [1:160] 1 1 1 1 2 2 2 2 3 3 ...
> >   .. ..$ Subplot   : num [1:160] 1 2 3 4 1 2 3 4 1 2 ...
> >
> > I should also mention that it's not always 4 points (subplots), and they
> > aren't always covering the same size area on the ground, so buffering by
> a
> > constant distance isn't the answer. I have subset out 3 plots (so 12
> > subplots) into a test file here:
> > https://dl.dropboxusercontent.com/u/72421241/test_subplotsToPlots.zip
> >
> > I have R version 3.3.0. I know it's customary to include code for what
> > I've tried, buuuut, that would be a blank canvas at this point. Googling
> > hasn't really been fruitful for this issue, so I thought you folks might
> > have some good ideas!
> >
> > Thanks,
> > Tina
> >
>
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>
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