R help - Jul 2009 - 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

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
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

It sounds like you might want to draw the convex hull for each group
of points.  There is a package called "chplot" which appears to
do this, though I haven't used it...

albyn

On Thu, Jul 16, 2009 at 06:23:54PM +0100, Ahmed, Sadia
wrote:
> 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  
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>