Illuminated contours

Wraps a contour layer, or any path layer, so that each segment is lit or shaded according to the direction of its slope relative to a light source. This is Kitiro Tanaka's illuminated-contour method. Lit segments are drawn in paper colour and shaded segments in ink. Both widen as the slope faces the light more directly. A hairline base contour is drawn under both. Over a geom_halftone() field or a hatched engraving, the paper segments cut through the screen and the surface appears in relief.

Usage

with_relief(
  layer,
  light = 315,
  width = c(0.05, 0.35),
  colours = c(lit = "white", shade = "black", base = "#8A8A8A"),
  uphill = c("auto", "left", "right")
)

# S3 method for class 'relief'
makeContent(x)

Arguments

layer

A geom_contour(), geom_path() or geom_line() layer; a list holding one; or a whole plot or patchwork, in which case every layer in it is wrapped. The object handed in is left alone.

light

Azimuth of the light in degrees, clockwise from north; 315 is upper left.

width

Line width in mm at grazing and at full illumination, c(min, max).

colours

Named vector: lit (the paper colour of the plot), shade (ink), base (the hairline contour under both; NA for none).

uphill

"auto", "left" or "right" of the path direction.

x

A relief grob (internal; makeContent method).

Value

The layer, with its geom replaced by a relief-drawing subclass.

Details

With uphill = "auto", the uphill side of each contour is inferred from the nearest neighbouring contour at another level. A closed ring with no such neighbour is treated as a summit. For a path that is not a contour, set uphill explicitly.

Draw this over a screened field. Lit segments are paper-coloured, so on bare paper they are invisible and only the shaded half of each contour appears.

References

Tanaka, K. (1950). The relief contour method of representing topography on maps. Geographical Review, 40(3), 444-456. doi:10.2307/211219

Examples

vol <- data.frame(expand.grid(x = seq_len(ncol(volcano)), y = seq_len(nrow(volcano))),
                   z = as.vector(t(volcano)))
ggplot2::ggplot(vol, ggplot2::aes(x, y, z = z)) +
  geom_halftone(shape = "line", colour = "black", angle = 30) +
    with_relief(ggplot2::geom_contour(bins = 10)) + ggplot2::coord_equal(expand = FALSE) +
  ggplot2::theme_bw() + theme_halftone()