Plot a soil texture triangle with sample points

Produces a ggplot2 object displaying a soil texture triangle with each texture class region drawn as a filled polygon and optional sample points overlaid. Triangle geometry is built from usda_texture_classes using an internal ternary-to-Cartesian coordinate conversion.

Usage

gg_texture_triangle(
  data,
  sand,
  silt,
  clay,
  colour = NULL,
  system = "USDA",
  style = c("none", "wiki"),
  breaks = c(20, 40, 60, 80),
  grid_colour = "grey70",
  grid_linetype = "dashed",
  grid_linewidth = 0.25,
  border_colour = "grey40",
  border_linewidth = 0.35,
  tick_height = NULL,
  surface = NULL,
  label_style = list()
)

Arguments

data

A data frame or tibble containing sample points to plot.

sand

Bare column name (or scalar) for sand percentage (0–100).

silt

Bare column name (or scalar) for silt percentage (0–100).

clay

Bare column name (or scalar) for clay percentage (0–100).

colour

Optional bare column name to map to point colour. Pass NULL (the default) for no colour mapping.

system

Classification system; currently only "USDA" is supported.

style

Fill colour style for texture class polygons. "none" (default) draws unfilled polygons; "wiki" applies the colour scheme used in the Wikipedia USDA soil texture diagram.

breaks

Numeric vector of percentage values at which to draw grid lines and tick marks (values between 1 and 99). Defaults to c(20, 40, 60, 80). Common alternatives: c(25, 50, 75) (quarters), seq(10, 90, 10) (deciles), seq(5, 95, 5) (5 % steps).

grid_colour

Colour of the internal grid lines. Defaults to "grey70".

grid_linetype

Line type of the internal grid lines. Defaults to "dashed". Any value accepted by ggplot2::geom_line() is valid (e.g. "solid", "dotted", "blank" to hide the grid entirely).

grid_linewidth

Stroke width of the internal grid lines. Defaults to 0.25.

border_colour

Colour of the texture class boundary lines. Defaults to "grey40". Set to NA to hide all class borders.

border_linewidth

Stroke width of the class boundary lines. Defaults to 0.35.

tick_height

Height of the tick marks drawn on each triangle edge, in Cartesian coordinate units. Defaults to NULL, which auto-scales with break density. Set to 0 to hide all tick marks while keeping grid lines and labels.

surface

Optional. A "texture_surface" object produced by texture_surface(), specifying a numeric variable to interpolate and display as a continuous fill gradient across the triangle. When supplied, any style palette fill is suppressed in favour of the surface; the fill scale is left unset so the user can control it freely with + ggplot2::scale_fill_*().
For iso-contour lines on top of the surface (or on a plain triangle), see geom_texture_contour().

label_style

Named list of text styling overrides. Prefer building this with texture_label_style() for argument completion and validation. Recognised keys:

tick_show

Show tick-mark percentage labels (default TRUE).

tick_size

Font size of tick labels. Defaults to auto-scale with break density (2.2 / 1.8 / 1.4 for ≤5 / ≤10 / >10 breaks).

axis_show

Show axis name labels (default TRUE).

axis_size

Font size of axis name labels (default 3.2).

class_show

Show texture class name labels inside polygons (default TRUE).

class_size

Font size of texture class labels (default 2.5).

Only the keys you supply are overridden; unspecified keys use defaults.

Value

A ggplot object.

Examples

soils <- data.frame(
  sand = c(70, 20, 40, 10),
  silt = c(15, 30, 40, 20),
  clay = c(15, 50, 20, 70)
)

# Defaults
gg_texture_triangle(soils, sand = sand, silt = silt, clay = clay)


# Wiki colours, 10 % grid, no class labels
gg_texture_triangle(soils, sand, silt, clay,
  style = "wiki", breaks = seq(10, 90, 10),
  label_style = list(class_show = FALSE))


# Solid grid in dark grey, hide tick labels
gg_texture_triangle(soils, sand, silt, clay,
  grid_colour = "grey40", grid_linetype = "solid",
  label_style = list(tick_show = FALSE))