Draws contour lines to depict the value of a function in ternary space.

TernaryContour(
Func,
resolution = 96L,
direction = getOption("ternDirection", 1L),
region = getOption("ternRegion", ternRegionDefault),
within = NULL,
filled = FALSE,
legend,
legend... = list(),
nlevels = 10,
levels = pretty(zlim, nlevels),
zlim,
color.palette = function(n) viridisLite::viridis(n, alpha = 0.6),
fill.col = color.palette(length(levels) - 1),
func... = list(),
...
)

## Arguments

Func

Function taking vectors of coordinates a, b and c, which returns a numeric vector whose value at each coordinate will be depicted.

resolution

The number of triangles whose base should lie on the longest axis of the triangle. Higher numbers will result in smaller subdivisions and smoother colour gradients, but at a computational cost.

direction

(optional) Integer specifying the direction that the current ternary plot should point: 1, up; 2, right; 3, down; 4, left.

region

(optional) Named list of length two specifying the the minimum and maximum values of each ternary axis to be drawn (e.g. list(min = c(40, 0, 0), max = c(100, 60, 60)); or a set of coordinates in a format accepted by TernaryPoints(). The plotted region will correspond to the smallest equilateral triangle that encompasses the specified ranges or coordinates.

within

List or matrix of x, y coordinates within which contours should be evaluated, in any format supported by xy.coords(x = within). If NULL, defaults to a region slightly smaller than the ternary plot. The \$hull entry generated by TriangleInHull() may also be used.

filled

Logical; if TRUE, contours will be filled (using .filled.contour().).

legend

Character vector specifying annotations for colour scale. If not provided, no colour legend is displayed. Specify TRUE to generate automatically, or a single integer to generate legend annotations.

legend...

List of additional parameters to send to SpectrumLegend().

nlevels, levels, zlim, ...

parameters to pass to contour().

color.palette

parameters to pass to .filled.contour().

fill.col

Sent as col parameter to .filled.contour(). Computed from color.palette if not specified.

func...

List of additional parameters to send to Func().

## Value

TernaryContour() invisibly returns a list containing:

• x,y: the Cartesian coordinates of each evaluated point;

• z: The value of Func() at each coordinate.

Other contour plotting functions: ColourTernary(), TernaryDensityContour(), TernaryPointValues()

## Examples

FunctionToContour <- function (a, b, c) {
a - c + (4 * a * b) + (27 * a * b * c)
}

# Set up plot
originalPar <- par(mar = rep(0, 4))
TernaryPlot(alab = "a", blab = "b", clab = "c")
values <- TernaryPointValues(FunctionToContour, resolution = 24L)
ColourTernary(
values,
legend = signif(seq(max(values), min(values), length.out = 4), 2),
bty = "n"
)
TernaryContour(FunctionToContour, resolution = 36L)

# Note that FunctionToContour is sent a vector.
BadMax <- function (a, b, c) {
max(a, b, c)
}

# Use
GoodMax <- function (a, b, c) {
pmax(a, b, c)
}
TernaryPlot(alab = "a", blab = "b", clab = "c")
ColourTernary(TernaryPointValues(GoodMax))
TernaryContour(GoodMax)

# Or, for a generalizable example,
GeneralMax <- function (a, b, c) {
apply(rbind(a, b, c), 2, max)
}
TernaryPlot(alab = "a", blab = "b", clab = "c")
# Fill the contour areas, rather than using tiles
TernaryContour(GeneralMax, filled = TRUE,
legend = c("Max", "...", "Min"), legend... = list(bty = "n"),
fill.col = viridisLite::viridis(14, alpha = 0.6))
# Re-draw edges of plot triangle over fill
TernaryPolygon(diag(3))

# Restore plotting parameters
par(originalPar)