Add gallery example showing how to adjust line segment ends (caps and joints) (#3015)

Co-authored-by: Dongdong Tian <[email protected]>
Co-authored-by: Michael Grund <[email protected]>

Author: 3 people

examples/gallery/lines/line_segment_ends.py

@@ -0,0 +1,76 @@
+"""
+Line segment caps and joints
+============================
+PyGMT offers different appearances of line segment caps and joints. The desired
+appearance can be set via the GMT default parameters :gmt-term:`PS_LINE_CAP`
+(``"butt"``, ``"round"``, or ``"square"`` [Default]) as well as :gmt-term:`PS_LINE_JOIN`
+(``"bevel"``, ``"round"``, and ``"miter"`` [Default]) and :gmt-term:`PS_MITER_LIMIT`
+(limit on the angle at the mitered joint below which a bevel is applied).
+"""
+
+# %%
+import numpy as np
+import pygmt
+
+# Set up dictionary for colors
+dict_col = {
+    "round": "green4",
+    "square": "steelblue",
+    "butt": "orange",
+    "miter": "steelblue",
+    "bevel": "orange",
+}
+
+# Create new Figure instance
+fig = pygmt.Figure()
+
+# -----------------------------------------------------------------------------
+# Top: PS_LINE_CAP
+
+# Create sample data
+x = np.array([30, 170])
+y = np.array([70, 70])
+
+fig.basemap(region=[0, 260, 0, 100], projection="x1p", frame="rltb")
+
+for line_cap in ["butt", "round", "square"]:
+    # Change GMT default locally
+    with pygmt.config(PS_LINE_CAP=line_cap):
+        color = dict_col[line_cap]
+        # Draw a 10-point thick line with 20-point long segments and gaps
+        # Use the local PS_LINE_CAP setting
+        fig.plot(x=x, y=y, pen=f"10p,{color},20_20")
+
+    # Draw a 1-point thick black solid line to highlight segment cap appearance
+    fig.plot(x=x, y=y, pen="1p,black,solid")
+    # Plot data points as circles
+    fig.plot(x=x, y=y, style="c0.1c", fill="white", pen="0.5p,")
+    # Add label for PS_LINE_CAP setting
+    fig.text(text=line_cap, x=x[-1] + 20, y=y[-1], justify="LM")
+
+    y = y - 20
+
+fig.shift_origin(yshift="-h")
+
+# -----------------------------------------------------------------------------
+# Bottom: PS_LINE_JOIN and PS_MITER_LIMIT
+
+x = np.array([5, 95, 65])
+y = np.array([10, 70, 10])
+
+fig.basemap(region=[0, 260, 0, 100], projection="x1p", frame="rltb")
+
+for line_join in ["bevel", "round", "miter"]:
+    with pygmt.config(PS_LINE_JOIN=line_join, PS_MITER_LIMIT=1):
+        color = dict_col[line_join]
+        # Draw a 7-point thick solid line
+        # Use the local PS_LINE_JOIN and PS_MITER_LIMIT settings
+        fig.plot(x=x, y=y, pen=f"7p,{color},solid")
+
+    fig.plot(x=x, y=y, pen="1p,black,solid")
+    fig.plot(x=x, y=y, style="c0.1c", fill="white", pen="0.5p")
+    fig.text(text=line_join, x=x[1] - 10, y=y[1], justify="RB")
+
+    x = x + 75
+
+fig.show()