[R] putting circles/buffers arround points on a 2D graph/plot

[Greg Snow]

Look at the chull function and its examples.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Ahmed, Sadia
> Sent: Thursday, July 16, 2009 11:24 AM
> To: r-help at r-project.org
> Subject: [R] putting circles/buffers arround points on a 2D graph/plot
> 
> Hi,
> 
> I'll try to keep my question brief and to the point, to anyone who
> helps 'THANK YOU!'
> 
> I want to get a circle/ring/buffer or some other form of drawn line
> around certain points on a x,y plot, the points usually don't form a
> circle, often they form a 'wobbly' shape, so ideally I'd like something
> that follows the shape the points make.
> 
> I'll start by explaining what I've got (I'm sorry if it's a little
> long, but it's all important for explaining what I want to do):
> 
> I have a simple 2D plot of an x variable, called 'percent.forest'', and
> a y variable called 'metric'. the data for this plot is in a large data
> frame with a third variable called 'Buffer', there are 5 buffer sizes
> (250, 500, 1000, 3000, 10000).
> 
> to create the plot I simply used
> >plot(percent.forest,metric)
> 
> to add in the data about buffer size, I have extracted the percent
> forest and metric data by:
> >buff250<-subset(data1,data1$Buffer==250)
> >buff500<-subset(data1,data1$Buffer==500)
> >buff1000<-subset(data1,data1$Buffer==1000)
> >buff3000<-subset(data1,data1$Buffer==3000)
> >buff10000<-subset(data1,data1$Buffer==10000)
> 
> i then used the 'points' function to plot the percent forest, metric
> data points in different colours according to buffer size, using this
> code (first 2 lines divides the data appropriately, 3rd line is
> points):
> >metric.250<-(log(buff250$metric))
> >percent.forest.250<-(buff250$percent.forest)
> >points(percent.forest.250,metric.250,col='skyblue')
> 
> I repeated this for all 5 buffer sizes, so on the plot
> (percent.forest,metric) the points are coloured differently according
> to the size of the buffer used.
> This works fine (the next bit is the problem):
> 
> Does anyone know how I can get R to draw around the different coloured
> points, so that i get 5 rings/wiggly lines on the plot that clearly
> shows the extent of each of the buffers, you can sort of see a pattern
> in the colours but its not as clear as it would be if I could draw
> around it).
> 
> If anyone wants to see a picture of the plot (if my explanation isn't
> clear enough) I'd be happy to email one directly to you (the R
> instructions says that the mailing list scraps attachments so I've not
> put one on here)
> 
> Thank you for reading this,
> Any help will be greatly appreciated,
> sadia
> 
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