Support passing string type numbers, geographic coordinates and datetimes

[seisman]

Description of proposed changes

This PR adds support for passing string type data to GMT via GMT_Put_Vectors. Supported string type data include:

• numeric strings (e.g., "0.5")
• geographic coordinates (e.g, "3:30W", "3:30N")
• datetime strings (e.g., 2010-01-01T00:00)

This PR should address the bug/feature request in #647 and #633.

To test this branch, you need GMT dev versions (i.e., GMT>=6.2.0). You can install the latest GMT dev versions using:

conda install -c conda-forge/label/dev gmt

Example script for testing:

import pygmt

fig = pygmt.Figure()
fig.basemap(region=[-10, 10, -10, 10], projection='M10c', frame=["WSEN", "afg1"])
fig.plot(x=5.0, y=5.0, style='c0.2c', color='red')
fig.plot(x='-5.0', y='-5.0', style='c0.2c', color='blue')
fig.plot(x='5:30W', y='5:30N', style='c0.2c', color='yellow')
fig.savefig("map.png")

Expected and actual output:

Fixes #647.
Fixes #633.

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.

Slash Commands

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

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[seisman]

/test-gmt-dev

[weiji14]

Can you add a doc API line at https://github.com/GenericMappingTools/pygmt/blame/v0.3.0/doc/api/index.rst#L214 for clib.Session.put_strings? Just realized we forgot to add it during #520.

[seisman]

Can you add a doc API line at v0.3.0/doc/api/index.rst#L214 (blame) for clib.Session.put_strings? Just realized we forgot to add it during #520.

Done in 24ad0af

[seisman]

See https://github.com/GenericMappingTools/pygmt/actions/runs/609196993 for the tests with GMT dev versions.

All the tests (including the new one) pass.

Tests with GMT 6.1.1 fails, because in the old codes, datetime strings can processed by pd.to_datetime, but now datetime strings are passed to GMT directly. As expected, passing datetime strings to GMT works for GMT dev but not GMT 6.1.1, so we can't merge the PR unless GMT 6.2.0 is released.

[seisman]

The idea of the test is to pass different combinations of strings to GMT, let GMT write it to a temporary file, and check if the output is the same as expected (i.e., if vector=expected_vetcor.

Still has trouble testing datetime strings, when the text file contains strings,

dtype=[("x", np.str_), ("y", np.str_)],

doesn't works as I expect.

[seisman]

Fixed in bf7587c, but could still be improved.

[seisman]

/test-gmt-dev

https://github.com/GenericMappingTools/pygmt/actions/runs/613257718

[weiji14]

Great to finally see this come through!