R: Erosion of a Hexagon Count Image

erode.hexbin {hexbin} | R Documentation

## Erosion of a Hexagon Count Image

### Description

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.

### Usage

    erode(hbin, cdfcut = 0.5)
    erode.hexbin(hbin, cdfcut = 0.5)

### Arguments

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

### Details

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.

### Value

An `"erodebin"` object (with all the slots from `hbin`) and additionally with high count cells and a component `erode` that gives the erosion order.

### See Also

`hexbin`, `smooth.hexbin`, `hcell2xy`, `gplot.hexbin`, `grid.hexagons`, `grid.hexlegend`

### Examples

    set.seed(153)
    x <- rnorm(10000)
    y <- rnorm(10000)
    bin <- hexbin(x,y)

    smbin  <- smooth.hexbin(bin)
    erodebin <- erode.hexbin(smbin, cdfcut=.5)
    plot(erodebin)

    ## bivariate boxplot
    hboxplot(erodebin, main = "hboxplot(erodebin)")

    # show erosion order
    plot(bin,style= "lat", minarea=1, maxarea=1,
         legend=FALSE, border=gray(.7))

    grid.hexagons(erodebin,style= "lat", minarea=1, maxarea=1,pen="green")
    xy <- hcell2xy(erodebin)
    library("grid")
    grid.text(lab = as.character(erodebin@erode), xy$x, xy$y,
              gp = gpar(col="white", cex=0.65))

[Package hexbin version 1.28.1 Index]