Ответ 1
Используя grid.raster
library(png)
flower <- readPNG("flower.png")
pushViewport(plotViewport(margins=c(5,5,5,5)))
grid.rect(gp = gpar(fill=NA))
pushViewport(plotViewport(margins=c(5,5,5,5),
xscale=extendrange(mydt$x),
yscale=extendrange(mydt$y)))
grid.raster(image=flower,x=mydt$x,y=mydt$y,width=mydt$z,
interpolate=FALSE,default.units = 'native')
grid.polyline(mydt$x,mydt$y,default.units='native')
upViewport(2)