Ternary Color Systems

pyrolite includes two methods for coloring data points and polygons in a ternary system, ternary_color() and color_ternary_polygons_by_centroid() which work well with some of the plot templates (pyrolite.plot.templates) and associated classifiers (pyrolite.util.classification).

import numpy as np
import matplotlib.pyplot as plt

Colors by Ternary Position

The ternary_color() function serves to generate the color which correpsonds the the mixing of three colours in proportion to the components in a ternary system. By default these colours are red, green and blue (corresponding to the top, left, and right components in a terarny diagram). The function returns colours in the form of an RGBA array:

from pyrolite.util.plot.style import ternary_color
from pyrolite.util.synthetic import normal_frame

# generate a synthetic dataset we can use for the colouring example
df = normal_frame(
    columns=["CaO", "MgO", "FeO"],
    size=100,
    seed=42,
    cov=np.array([[0.8, 0.3], [0.3, 0.8]]),
)

colors = ternary_color(df)
colors[:3]

array([[0.18902861, 0.54222697, 0.26874443, 0.999999  ],
       [0.5097609 , 0.16739226, 0.32284684, 0.999999  ],
       [0.08310658, 0.37115312, 0.54574029, 0.999999  ]])

These can then be readily used in a ternary diagram (or eleswhere):

ax = df.pyroplot.scatter(c=colors)
plt.show()

ax = df[["MgO", "CaO"]].pyroplot.scatter(c=colors)
plt.show()

You can use different colors for each of the verticies if you so wish, and mix and match named colors with RGB/RGBA represntations (note that the alpha will be scaled, if it is passed as a keyword argument to ternary_color()):

colors = ternary_color(df, alpha=0.9, colors=["green", "orange", [0.9, 0.1, 0.5, 0.9]])
ax = df.pyroplot.scatter(c=colors)
plt.show()

Colors by Centroid Position

We can also colour polygons within one of these templates by the ternary combination of colours (defaulting to red, green and blue) at the polygon centroid:

from pyrolite.util.classification import USDASoilTexture
from pyrolite.util.plot.style import color_ternary_polygons_by_centroid

clf = USDASoilTexture()
ax = clf.add_to_axes(ax=None, add_labels=True, figsize=(8, 8))
color_ternary_polygons_by_centroid(ax)
plt.show()

There are a range of options you can pass to this function to control the ternary colors (as above), change the scaling coefficients for ternary components and change the opacity of the colors:

color_ternary_polygons_by_centroid(
    ax, colors=("red", "green", "blue"), coefficients=(1, 1, 1), alpha=0.5
)
plt.show()