R: Panel functions for level-coded irregular points

panel.voronoi {latticeExtra} | R Documentation

## Panel functions for level-coded irregular points

### Description

These panel functions for `levelplot` can represent irregular (x, y) points with a color covariate. `panel.levelplot.points` simply draws color-coded points. `panel.voronoi` uses the deldir package to calculate the spatial extension of a set of points in 2 dimensions. This is known variously as a Voronoi mosaic, a Dirichlet tesselation, or Thiessen polygons.

### Usage

    panel.voronoi(x, y, z, subscripts = TRUE, at = pretty(z),
       points = TRUE, border = "transparent",
       na.rm = FALSE, win.expand = 0.07, use.tripack = FALSE,
       ...,
       col.regions = regions$col, alpha.regions = regions$alpha)

    panel.levelplot.points(x, y, z, subscripts = TRUE, at = pretty(z),
       shrink, labels, label.style, contour, region,
       pch = 21, col.symbol = "#00000044",
       ...,
       col.regions = regions$col, fill = NULL)

### Arguments

`x, y, z` | an irregular set of points at locations (x, y) with value z.
`subscripts` | integer vector indicating what subset of x, y and z to draw. Typically passed by `levelplot`.
`at, col.regions, alpha.regions` | color scale definition; see `panel.levelplot`.
`points` | whether to draw the (x, y) points.
`border` | color for polygon borders.
`na.rm` | if `TRUE`, points with missing `z` values will be excluded from the calculation of polygons. If `FALSE`, those polygons are calculated but are not drawn (i.e. are transparent).
`win.expand` | defines the rectangular window bounding the polygons. This is a factor by which to expand the range of the data. Set to 0 to limit drawing at the furthest data point locations. Ignored if `use.tripack = TRUE`.
`use.tripack` | if `TRUE`, use tripack package rather than deldir. See Details.
`...` | further arguments are passed to `panel.xyplot` if `points = TRUE`.
`pch, col.symbol` | symbol and border color for points. A filled symbol should be used, i.e. in the range 21-25.
`shrink, labels, label.style, contour, region, fill` | ignored.

### Details

The tripack package implementation is faster than deldir but not under a fully free licence. Also, the deldir package allows polygons to be clipped to a rectangular window (the `win.expand` argument).

### Author(s)

Felix Andrews felix@nfrac.org

### See Also

`tileplot`, `panel.levelplot`, `deldir`

### Examples

    ## a variant of Figure 5.6 from Sarkar (2008)
    ## http://lmdvr.r-forge.r-project.org/figures/figures.html?chapter=05;figure=05_06

    depth.ord <- rev(order(quakes$depth))
    quakes$Magnitude <- equal.count(quakes$mag, 4)
    quakes.ordered <- quakes[depth.ord, ]

    levelplot(depth ~ long + lat | Magnitude, data = quakes.ordered,
             panel = panel.levelplot.points, type = c("p", "g"),
             aspect = "iso", prepanel = prepanel.default.xyplot)

    ## a levelplot with jittered cells

    xyz <- expand.grid(x = 0:9, y = 0:9)
    xyz[] <- jitter(as.matrix(xyz))
    xyz$z <- with(xyz, sqrt((x - 5)^2 + (y - 5)^2))
    levelplot(z ~ x * y, xyz, panel = panel.voronoi, points = FALSE)

    ## hexagonal cells

    xyz$y <- xyz$y + c(0, 0.5)
    levelplot(z ~ x * y, xyz, panel = panel.voronoi, points = FALSE)

[Package latticeExtra version 0.6-28 Index]