Multicolored points in plot [duplicate] - r

Question

This question already has answers here:
Plotting half circles in R
(3 answers)
Closed 2 years ago.
I'd like to add points that are multicoloured dots, with one half in blue for ex. and one half in red. If possible, I'd like to be able to do it with more than 2 colors, for example 4 quarters, each with a color.
Is that at all possible?
I know I can superimpose several dots of different sizes, each with a color, resulting in a concentric multicolored dot. But this is not what I am after.
For context, I am using these points for cities in a map.
Here is a small example, with each city having a unicolored dot. But I would like each city to have a dot that has two halves, each one with a color.
require(ggmap);
citiesnames=c("Madrid","Toledo","Valencia","Granada")
cities=str_c(citiesnames,"Spain",sep=", ");
geo=geocode(cities);
lon=geo$lon;
lat=geo$lat;
coord=mapproject(lon, lat,proj="mercator");
map("world","Spain",fill=T,col="ivory",proj="mercator");
points(coord$x[1], coord$y[1], pch=16, cex=1.2, col="black")
points(coord$x[2],coord$y[2], pch=16, cex=1.2, col="red")
points(coord$x[3], coord$y[3], pch=16, cex=1.2, col="blue")
points(coord$x[4], coord$y[4], pch=16, cex=1.2, col="green4")
Any help greatly appreciated.

Answer 1

As I mentioned in the comments you can refer to this post for doing what you want. For documentation purposes I add an answer which resolve the issue:
You can add two half circles (pie charts) to your graph using these two functions:
upper.half.circle <- function(x,y,r,nsteps=100,...){
rs <- seq(0,pi,len=nsteps)
xc <- x+r*cos(rs)
yc <- y+r*sin(rs)
polygon(xc,yc,...)
}
lower.half.circle <- function(x,y,r,nsteps=100,...){
rs <- seq(0,pi,len=nsteps)
xc <- x-r*cos(rs)
yc <- y-r*sin(rs)
polygon(xc,yc,...)
}
Later when you are piloting you should set asp = 1 to get the half-circles.
plot(1, type="n",axes=F,xlab="", ylab="",xlim=c(0,200),ylim=c(0,200), asp = 1)
upper.half.circle(15,170,10,nsteps=1000,col='red')
lower.half.circle(15,170,10,nsteps=1000,col='blue')
Here's the result of this code:
You can later edit the fictions for getting quarters or whatever you need.