On 03/05/2011 07:25 PM, Greg Snow wrote:
It is not completely clear what you are trying to accomplish. Do you want to
draw a shape in the plot then identify all the points in that shape? You could
use locator (with type='l') to draw a polygon, then there are functions in add
on packages (mostly the spatial ones) that will detect which points are within
a polygon that you could use with the raw data and the polygon created.
If that is not what you want, then maybe describe your goals in more detail
(examples are good if you can give one).
Thats exactly what I want. drawing a polygon in a plot and searching for
the points inside the polygon. I managed to create that polygon and to
check which points are inside but only by supplying my function with the
coordinates of the points. Now I was wondering whether it is also
possible to retrieve these coordinates from the plot (similar to
par()$usr and similar...).
ideally it would work as follows:
x<-rnorm(20)
y=rnorm(20)
plot(x,y)
points.in.poly <- identify.poly() #see below
#now click on the plot to identify the points
Right now it only works like
points.in.poly <- identify.poly(x,y)
Anyway, supplying the points is not too complicated, it would just be
easier to do without.
identify.poly <- function(x,y,col.points='red')
{
require(sp)
exit=FALSE
i=0
coords.all <- list(x=vector(length=100),y=vector(length=100))
coords.all$x[1:100]<-NA
coords.all$y[1:100]<-NA
while (i<100)
{
coords.t <- locator(n=1)
exit=!point.in.polygon(coords.t$x,coords.t$y,
par()$usr[c(1,2,2,1)],par()$usr[c(3,3,4,4)])
if (exit)
{
break
}
i=i+1
points(coords.t,col=col.points,pch='+')
coords.all$x[i] <- coords.t$x
coords.all$y[i] <- coords.t$y
if (i>1)
points(coords.all$x[(i-1):i],coords.all$y[(i-1):i],lty=2,
col=col.points,type='l')
}
points(coords.all$x[c(i,1)],coords.all$y[c(i,1)],lty=2,
col=col.points,type='l')
coords.all$x <- na.omit(coords.all$x)
coords.all$y <- na.omit(coords.all$y)
points.inpoly <- point.in.polygon(point.x=x,point.y=y,
pol.x=coords.all$x,pol.y=coords.all$y)
points(x[points.inpoly==1],y[points.inpoly==1],pch=par()$pch,col=col.points)
data.return=list(in.poly=!!points.inpoly,x=x,y=y)
}
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