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.

1 2 3 4 5 6 7 8 9 10 11 | ```
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)
``` |

`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 |

`at, col.regions, alpha.regions` |
color scale definition;
see |

`points` |
whether to draw the (x, y) points. |

`border` |
color for polygon borders. |

`na.rm` |
if |

`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` |
if |

`...` |
further arguments are
passed to |

`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. |

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).

Felix Andrews felix@nfrac.org

`tileplot`

,
`panel.levelplot`

,
`deldir`

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | ```
## 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)
``` |

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