Add examples for plotting lines

[seisman]

Description of the desired feature

There are already have nice tutorials for plotting data points of various sizes and colors, but no examples for plotting lines.

It would be good to add some examples showing

• how to plot lines
• how to specify line attributes (pen thickness, color, and pen style)
• plot lines with various colors as determined by a CPT file

Unfortunately, PyGMT currently can't handle multi-segments data as in GMT. To plot multiple lines, we still have to call fig.plot() multiple times.

[seisman]

#604 (comment)

Also, was just looking at the GMT.jl AGU gallery examples at https://www.generic-mapping-tools.org/GMT.jl/latest/gallery/tables/, looks like there's a lot of decorated arrows/curved line examples we can follow.

[willschlitzer]

I'll work on this.

[willschlitzer]

I'm trying to figure out how to add a specific CPT, but I'm not getting it to plot on the actual line. I tried setting a specific CPT to cmap, and also tried adding "red,green" to add specific colors, but no luck.

[weiji14]

Yeah it's complicated, took me a while to figure it out recently too. Try this for inspiration:

import pygmt
import numpy as np

fig = pygmt.Figure()
fig.basemap(frame=["WSne", "af"], region=[20, 30, -10, 10])
pygmt.makecpt(cmap="batlow", series=[0, 10, 1])
x = np.arange(start=20, stop=30, step=0.2)
for zvalue in range(0, 10):
    y = zvalue * np.sin(x)
    fig.plot(x=x, y=y, cmap=True, zvalue=zvalue, pen=f"thick,+z,-")

fig.show()

[willschlitzer]

@weiji14 Impressive find, but that seems like a big step up in complexity from the rest of the tutorial. I've been out of geoscience for 8+ years so I don't keep up with what people want in their plots, but this seems out of place for a basic "How to plot lines" tutorial. My opinion is something like this belongs in a gallery example.

[willschlitzer]

@seisman Are you looking to have anything else added to these line plotting examples before closing the issue? As stated above, I think the custom CPT example provided by @weiji14 may be a bit advanced for a basic tutorial.

[seisman]

@weiji14's example is pretty good and could be added to the gallery (https://www.pygmt.org/dev/gallery/index.html#lines).