Skip to contents

Plot a USDA soil texture triangle (ternary diagram)

Source: R/texture.R
texture_triangle.Rd

Creates a USDA texture triangle with filled texture-class regions, USDA class boundary lines, class name labels, and optional data points — all using a pure ggplot2 ternary-to-Cartesian projection (Clay at top, Sand at bottom-left, Silt at bottom-right). No external ternary-plot package is required.

Usage

texture_triangle(
  df,
  sand_col = "sand_total",
  silt_col = "silt",
  clay_col = "clay",
  color_col = NULL,
  title = "Soil Texture Triangle",
  point_size = 3,
  alpha = 0.85
)

Arguments

df

A data frame.

sand_col

Column name for sand (default "sand_total").

silt_col

Column name for silt (default "silt"). Used only for data point projection; silt for the background grid is derived as 100 - clay - sand.

clay_col

Column name for clay (default "clay").

color_col

Column name for colouring data points (default NULL — points are drawn in black). If the column contains USDA texture class names the same USDA palette is applied automatically.

title

Plot title.

point_size

Point size (default 3.0).

alpha

Point transparency (default 0.85).

Value

A ggplot object.

Details

The background is always coloured by USDA texture class (12-class USDA-inspired palette). Data points are overlaid and can be mapped to a separate variable via color_col.

Examples

df <- data.frame(sand_total = c(70, 20, 10, 40),
                 silt       = c(15, 50, 30, 40),
                 clay       = c(15, 30, 60, 20),
                 Texture    = c("Sandy Loam", "Silt Loam", "Clay", "Loam"))
texture_triangle(df, color_col = "Texture")