Figure.meca: Add aliases for "Fa", "Fe", "Fg", "Ft", "Fp"

[yvonnefroehlich]

Description of proposed changes

This PR adds aliases for the GMT flags used for plotting the P and T axes for Figure.meca:

GMT flag	PyGMT alias
Fa	pt_axes
Fe	t_axisfill
Fg	p_axisfill
Ft	t_axispen
Fp	p_axispen

The docstrings are orientated on the upstream GMT documentation at https://docs.generic-mapping-tools.org/dev/supplements/seis/meca.html#f.

Preview: https://pygmt-dev--3526.org.readthedocs.build/en/3526/api/generated/pygmt.Figure.meca.html

Fixes #

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 wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code

[seisman]

I'm wondering if we can make these parameters more Pythonic. Could you please provide a minimal example so that anyone interested can play with these parameters?

[yvonnefroehlich]

First of all, I have never used this feature my own yet, and this PR was mainly motivated by a question on the GMT forum xD

Could you please provide a minimal example so that anyone interested can play with these parameters?

The following example is modified from the example I posted on the GMT forum (https://forum.generic-mapping-tools.org/t/add-p-t-axis-to-focal-mechanism/5464/2?u=yvonnefroehlich) and is based on my current understanding of the upstream GMT docs:

import pygmt
import numpy as np

size = 5

fig = pygmt.Figure()
fig.basemap(region=[-size, size] * 2, projection=f"X{size}c", frame=0)

fig.meca(
    spec=np.array([0, 0, 0,  35, 42, 70, 5]),  # lon, lat, dep,  strike, dip, rake, magnitude
    scale="4c+m",
    convention="aki",
    Fa="0.5c/cd",  # Compute and plot P and T axes with symbols, Adjust size and symbols
    Fe="pink",  # Adjust fill of T axis symbol
    Fg="cyan",  # Adjust fill of P axis symbol
    Ft="2p,red",  # Adjust outline of T axis symbol
    Fp="2p,blue",  # Adjust outline of P axis symbol
)

fig.show()

[yvonnefroehlich]

I'm wondering if we can make these parameters more Pythonic

Hm, yeah, I needed a moment to sort all these flags... and made a rough overview (probably not perfect):

• W -> pen (adjust circumference, set default for all lines)
• Fa -> pt_axes (add and set size and symbols for P and T axes)

quadrants (aliases existing)	axes (aliases added in this PR)
G -> compressionfill [Default is "black"]	Fg -> p_axisfill [Default is G]
E -> extensionfill [Default is "white"]	Fe -> t_axisfill [Default is E]
L -> outline [Default is W]	Fp -> p_axispen [Default is W]
T -> nodal [Default is W]	Ft -> t_axispen [Default is W]

The argumente passed to Fa can be confusing because there is no slash (/") between the two symbol codes (e.g., "0.5c/cd").

Besides these parameters, there are

• A -> offset [Default for the line is W, Default for the fill is G or C]
• Fr -> labelbox [Default for the fill is "white"]