erode.hexbin {hexbin}R Documentation

Erosion of a Hexagon Count Image


This erosion algorithm removes counts from hexagon cells at a rate proportional to the cells' exposed surface area. When a cell becomes empty, algorithm removes the emptied cell and notes the removal order. Cell removal increases the exposure of any neighboring cells. The last cell removed is a type of bivariate median.


erode.hexbin(bin, cdfcut = 0.5)


bin an object of class hexbin.
cdfcut number in (0,1) indicating the confidence level for the limits.


The algorithm extracts high count cells with containing a given fraction (cdfcut) of the total counts. The algorithm extracts all cells if cdfcut=0. The algorithm performs gray-level erosion on the extracted cells. Each erosion cycle removes counts from cells. The counts removed for each cell are a multiple of the cell's exposed-face count. The algorithm choses the multiple so at least one cell will be empty or have a count deficit on each erosion cycle. The erode vector contain an erosion number for each cell. The value of erode is

6*erosion_cycle_ at_ cell_ removal - cell_deficit_at_removal

Cells with low values are eroded first. The cell with the highest erosion number is a candidate bivariate median. A few ties in erode are common.


A bin object with high count cells and a component called erode that gives the erosion order.

See Also

hexbin, smooth.hexbin, hcell2xy, hcell, plot.hexbin, hboxplot, hdiffplot, hmatplot, hexagons, hex.legend


x <- rnorm(10000)
y <- rnorm(10000)
bin <- hexbin(x,y)

## bivariate boxplot
smbin  <- smooth.hexbin(bin)
erodebin <- erode.hexbin(smbin,cdfcut=.5)

# show erosion order
oldpar <- par(no.readonly=TRUE)
screenpar <- plot.hexbin(bin,style= "lat", minarea=1, maxarea=1,
                         legend=FALSE, border=gray(.7))
par(screenpar)      # reset to the plot on the screen

hexagons(erodebin,style= "lat", minarea=1, maxarea=1,pen="green")
xy <- hcell2xy(erodebin)
text(xy, lab = as.character(erodebin$erode),col="white",cex=.65)

[Package hexbin version 1.0.10 Index]