distance <- function(x1,y1,x2,y2) sqrt((x1-x2)^2+(y1-y2)^2)
aligned <- function(x1,y1,x2,y2,x3,y3,e) abs(distance(x1,y1,x2,y2)-distance(x1,y1,x3,y3))<e
db<-read.csv(file="C:\\coordinates.csv",sep=";",header=T) 
attach(db)

point1 <- 35
point2 <- 47
e <- 10 

plot(x,y,col="light gray")
points(x[point1],y[point1],pch=19,col="dark red")
points(x[point2],y[point2],pch=19,col="dark red")
text(x[point1],y[point1],name[point1],cex=0.7,pos=1)
text(x[point2],y[point2],name[point2],cex=0.7,pos=1) 

for(i in 1:length(x))
{
  if(i!=point1 & i!=point2)
  if(aligned(x[point1],y[point1],x[point2],y[point2],x[i],y[i],e))
  {
    points(x[i],y[i],pch=19,col="dark blue")
    text(x[i],y[i],name[i],cex=0.5,pos=1)
  }
}