How do I plot a circle with points inside it in R?

Question

I need to plot a circle centered at (0,0) in R. Then I would like to plot points in that circle specified in radius and degrees. Could anyone point me in the right direction for this task?

Do you mean *radius* and degrees? – James Dec 12 '11 at 10:58 — James, Dec 12 '11 at 10:58

score 4 · Accepted Answer · answered Dec 12 '11 at 11:47

In base graphics:

r <- 3*runif(10)
degs <- 360*runif(10)

# First you want to convert the degrees to radians

theta <- 2*pi*degs/360

# Plot your points by converting to cartesian

plot(r*sin(theta),r*cos(theta),xlim=c(-max(r),max(r)),ylim=c(-max(r),max(r)))

# Add a circle around the points

polygon(max(r)*sin(seq(0,2*pi,length.out=100)),max(r)*cos(seq(0,2*pi,length.out=100)))

Note that at least one of the points will be on the border of the circle, so if you dont want this you would have replace of the max(r) statments with something like 1.1*max(r)

Add `, asp = 1` to the plot statement for the final image to display as a circle instead of an oval. — Mark Miller, Sep 13 '13 at 22:29

score 2 · Answer 2 · answered Dec 12 '11 at 10:59

2

To do this with ggplot2, you need to use coord_polar, ggplot2 will do all the transformations for you. An example in code:

library(ggplot2)
# I use the builtin dataset 'cars'
# Normal points plot
ggplot(aes(x = speed, y = dist), data = cars) + geom_point()

enter image description here

# With polar coordinates
ggplot(aes(x = speed, y = dist), data = cars) + geom_point() + 
     coord_polar(theta = "dist")

enter image description here

answered Dec 12 '11 at 10:59

Paul Hiemstra

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Thanks, that looks perfect, but I keep getting `Error in match.arg(theta, c("x", "y")) : 'arg' should be one of “x”, “y”` – wfbarksdale Dec 12 '11 at 11:04
the problem with this is that I can't specify location in degrees – wfbarksdale Dec 12 '11 at 11:39
Please post a reproducible example if you want more to the point feedback. – Paul Hiemstra Dec 12 '11 at 11:47
That example will work if `coord_polar(theta = "dist")` is changed to `coord_polar(theta = "y")` – samhiggins2001 May 29 '14 at 19:36

Yuriy Vikulov · Answer 3 · 2011-12-12T11:01:11.150

0

Use a polar system of coords.(link to wiki).

then transle it into Cartesian coordinate system (link)

and then translate to screen coords ( for example 0,0 is a center of your monitor)

edited Dec 12 '11 at 11:01

answered Dec 12 '11 at 10:55

Yuriy Vikulov

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How do I plot a circle with points inside it in R?

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