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

`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 0.6-25 Index]