清除R中的绘图点

Question

I am trying to use the animation package to generate an "evolving" plot of points on a map. The map is generated from shapefiles (from the readShapeSpatial/readShapeLines functions).

The problem is when it's plotted in a for loop, the result is additive, whereas the ideal result is to have it evolve.

Are there ways of using par() that I am missing?

My question is: is there a way to clear just the points ploted from the points function and not clearing the entire figure thus not having to regraph the shapefiles?

in case someone wants to see code:

# plotting underlying map
newyork <- readShapeSpatial('nycpolygon.shp')
routes <- readShapeLines('nyc.shp')
par(bg="grey25")
plot(newyork, lwd=2, col ="lightgray")
plot(routes,add=TRUE,lwd=0.1,col="lightslategrey")

# plotting points and save to GIF
ani.options(interval=.05)
saveGIF({
  par(bg="grey25")
  # Begin loop
  for (i in 13:44){
    infile <-paste("Week",i,".csv",sep='')
    mydata <-read.csv(file = infile, header = TRUE, sep=",")
    plotvar <- Var$Para
    nclr <- 4
    plotclr <-brewer.pal(nclr,"RdPu")
    class<- classIntervals(plotvar,nclr,style = "pretty")
    colcode <- findColours(class,plotclr)
    points(Var$Lon,Var$Lat,col=colcode)
  }
})

Answer 1

If you can accept a residual shadow or halo of ink, you can over-plot with color ="white" or == to your background choices. We cannot access your shape file but you can try it out by adding this line:

points(Var$Lon, Var$Lat, col="grey25")

It may leave gaps in other previously plotted figures or boundaries, because it's definitely not object-oriented. The lattice and ggplot2 graphics models are more object oriented, so if you want to post a reproducible example, that might be an alternate path to "moving" forward. I seem to remember that the rgl package has animation options in its repetoire.