Multiple legends in spplot

Lee,

looking at sp:::SpatialPolygons2Grob, you can exactly see what this
function wants and does with it. As a (second) legend involves not only
polygons, but also points, symbols, and text, it will not do the job.

An ad-hoc solution to this would be, building on your well-prepared
example and the code present in package sp:

mapLegendGrob2 <- function(obj, widths = unit(1, "cm"), heights =
unit(1, "cm"), fill = "black", just = "right", labels) {
    grb1 = SpatialPointsLegend(obj, fill = fill)
    grb2 = TextLegend(labels)
    key.layout <- grid.layout(nrow = 1, ncol = 1, widths = widths,
                    heights = heights, respect = TRUE, just = just)
    key.gf <- frameGrob(layout = key.layout)
#   key.gf <- placeGrob(key.gf,
#                 rectGrob(gp = gpar(fill = "transparent", col = NULL)),
#                 row = NULL, col = NULL)
    key.gf <- placeGrob(key.gf, grb1, row = 1, col = 1)
    key.gf <- placeGrob(key.gf, grb2, row = 1, col = 1)
    key.gf
}

TextLegend = function(labels, dist = 0.5) {
    x = rep(dist, length(labels))
    y = 1:length(labels)
    textGrob(labels, x, y, just = "left")
}
SpatialPointsLegend = function(pch, fill) {
    x = rep(0, length(pch))
    y = 1:length(pch)
    pointsGrob(x=x, y=y, pch=pch, gp = gpar(fill = fill))
}
spplot(spdfMeuse,
    sp.layout = list("sp.points", meuse, pch = as.integer(meuse $soil)),
    legend = list(inside = list(fun = mapLegendGrob2(1:3, fill=1:3,

    labels=c("a","b","c")), x = 1, y = 0.1, corner = c(0,0)))
)

I'm not very familiar with the functions in package grid, so there might
be lots of room for improvement. A more generic solution would be very
welcome, but this might get you somewhat further.

Multiple legends in spplot

Thread (3 messages)