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 PS_LINE_CAP ("butt", "round", or "square" [Default]) as well as PS_LINE_JOIN ("bevel", "round", and "miter" [Default]) and 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()