Add gallery example for Figure.ternary method

examples/gallery/embellishments/ternary.py

@@ -0,0 +1,48 @@
+"""
+Ternary diagram
+---------------
+The pygmt.Figure.ternary method can draw ternary diagrams. The example shows
+how to plot circles with a diameter of 0.1 centimeters (``style=0.1c``) on a
+10-centimeter-wide (```width=10c``) ternary diagram at the positions listed
+in the first three columns of the sample dataset `rock_compositions`, with
+default annotations and gridline spacings, using the specified labeling
+defined via ``alabel``, ``blabel`` and ``clabel``. Points are colored based
+on the values given in the fourth columns of the sample dataset via
+``cmap=True``.
+"""
+
+import pygmt
+
+fig = pygmt.Figure()
+
+# Load sample data
+data = pygmt.datasets.load_sample_data(name="rock_compositions")
+
+# Define a colormap to be used for the values given in the fourth column
+# of the input dataset
+pygmt.makecpt(cmap="batlow", series=[0, 80, 10])
+
+fig.ternary(
+    data,
+    region=[0, 100, 0, 100, 0, 100],
+    width="10c",
+    style="c0.1c",
+    alabel="Limestone",
+    blabel="Water",
+    clabel="Air",
+    cmap=True,
+    frame=[
+        "aafg+lLimestone component+u %",
+        "bafg+lWater component+u %",
+        "cagf+lAir component+u %",
+    ],
+)
+
+# Shift origin -1 centimeters in y direction to avoid overlap
+# between ternary diagram and colorbar
+fig.shift_origin(yshift="-1c")
+
+# Add a colorbar indicating the values given in the fourth column of
+# the input dataset
+fig.colorbar(frame=["x+lPermittivity"])
+fig.show()