Improve the gallery example for line styles

[seisman]

Description of proposed changes

Old example	New example

Address the comment in #604 (comment).

Preview: https://pygmt-git-improve-linestyle.gmt.vercel.app/gallery/line/linestyles.html

The last line (white/black railway track style) is a little tricky. I like it but I'm OK if you think we should remove it.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

[weiji14]

The new example looks great, especially with the text labels!

[weiji14]

Could we avoid using a for-loop here as there are some things here like y -= 1 and x[-1] which might not be as readable for beginner Python users. It will make the code longer, but I think it's worth showing things more explicitly.

[seisman]

I think these are very basic syntax even for Python beginners. Perhaps only changing y -= 1 to y = y - 1 is enough?

[weiji14]

How about using a dictionary and doing a for-loop through different y values? Something like

for y, linestyle in {1: "1p,red,-", 2: "1p,blue,.", ...}.items():
    fig.plot(...)
    fig.text(...)

The x values can be hardcoded since they're always the same (0 to 9). Only the y is changing.

[seisman]

Looping over a dictionary seems a more advanced technique. What about using x[1] and y[1] (or x[0] and y[0] for left-side labels)?

[weiji14]

On second thought, I think the for-loop is fine as is.

Went down a rabbit hole of doing quoted lines following https://docs.generic-mapping-tools.org/latest/cookbook/contour-annotations.html, but somehow I couldn't escape the colon : character on the tomato line:

fig = pygmt.Figure()
fig.basemap(region=[0, 10, 0, 10], projection="X15c/8c", frame='+t"Line Styles"')

# Plot the line using the default line style
fig.plot(x=x, y=y)
fig.text(x=x[-1], y=y[-1], text="solid (default)", justify="ML", offset="0.2c/0c")

## Plot the line using different line styles
# dashed line
fig.plot(x=x, y=y - 1, pen="1p,red,-", style='qn1:+l" 1p,red,- "')
# dotted line
fig.plot(x=x, y=y - 2, pen="1p,blue,.", style='qn1:+l" 1p,blue,. "')

# dash-dotted line
fig.plot(x=x, y=y - 3, pen="1p,lightblue,-.", style='qn1:+l" 1p,lightblue,-. "')
# dot-dot-dashed line
fig.plot(x=x, y=y - 4, pen="2p,blue,..-", style='qn1:+l" 2p,blue,..- "')

# dash-dash-dotted line
fig.plot(x=x, y=y - 5, pen="2p,tomato,--.", style='qn1:+l" 2p,tomato,--. "')
# A pattern of 4-point-long line segment and 2-point-gap between segment
fig.plot(x=x, y=y - 6, pen="2p,tomato,4_2:2p", style=r'qn1:+l" 2p,tomato,4_2\:2p "')
fig.show()

[weiji14]

On second thought, I think the for-loop is fine as is.

Went down a rabbit hole of doing quoted lines following https://docs.generic-mapping-tools.org/latest/cookbook/contour-annotations.html, but somehow I couldn't escape the colon : character on the tomato line:

fig = pygmt.Figure()
fig.basemap(region=[0, 10, 0, 10], projection="X15c/8c", frame='+t"Line Styles"')

# Plot the line using the default line style
fig.plot(x=x, y=y)
fig.text(x=x[-1], y=y[-1], text="solid (default)", justify="ML", offset="0.2c/0c")

## Plot the line using different line styles
# dashed line
fig.plot(x=x, y=y - 1, pen="1p,red,-", style='qn1:+l" 1p,red,- "')
# dotted line
fig.plot(x=x, y=y - 2, pen="1p,blue,.", style='qn1:+l" 1p,blue,. "')

# dash-dotted line
fig.plot(x=x, y=y - 3, pen="1p,lightblue,-.", style='qn1:+l" 1p,lightblue,-. "')
# dot-dot-dashed line
fig.plot(x=x, y=y - 4, pen="2p,blue,..-", style='qn1:+l" 2p,blue,..- "')

# dash-dash-dotted line
fig.plot(x=x, y=y - 5, pen="2p,tomato,--.", style='qn1:+l" 2p,tomato,--. "')
# A pattern of 4-point-long line segment and 2-point-gap between segment
fig.plot(x=x, y=y - 6, pen="2p,tomato,4_2:2p", style=r'qn1:+l" 2p,tomato,4_2\:2p "')
fig.show()

[seisman]

somehow I couldn't escape the colon : character on the tomato line:

Looks like another upstream bug. Here is a minimum bash script to reproduce the bug.

gmt plot -R0/10/0/10 -JX10c -Sqn1:+lA:B -W2p,tomato,4_2:2p -pdf map << EOF
0  5
10 5
EOF

[weiji14]

LGTM!

[seisman]

gmt plot -R0/10/0/10 -JX10c -Sqn1:+lA:B -W2p,tomato,4_2:2p -pdf map << EOF
0 5
10 5
EOF

FYI, I opened a bug report in upstream GMT (GenericMappingTools/gmt#4369).