Add pygmt.load_dataarray function and refactor modules that return None or xarray.dataarray

[maxrjones]

Description of proposed changes

This PR adds a new pygmt/io.py module that holds process_output_grid, which returns an xarray.DataArray or None depending on whether outgrid matches tmpfile.name.

It replaces duplicate code with the new function.

Fixes #1400

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

[willschlitzer]

Looks great!

[weiji14]

Hi @meghanrjones, hoping that you can spend some time working on this PR soon (since there's a lot of open PRs that could benefit from a standardized function)! Based on the discussion above at #1439 (comment), here are some suggested changes. You'll also need to:

1. Update doc/api/index.rst to include the new load_datagrid function. My thought was to place it under 'Data Processing', but we could start a dedicated Input/output section in the API docs if you prefer, similar to https://geopandas.org/docs/reference/io.html. You'll also need to add from pygmt.io import load_datagrid to pygmt/__init__.py.

Input/Output:

.. autosummary::
    :toctree: generated

    load_datagrid

2. Find and replace process_output_grid to load_datagrid across all the grd* functions. Remember to also include grdproject added recently in Wrap grdproject #1377 and load_earth_relief at

   pygmt/pygmt/datasets/earth_relief.py

   Lines 136 to 138 in ebbb0cc

   	with xr.open_dataarray(fname, engine="netcdf4") as dataarray:
   	grid = dataarray.load()
   	_ = grid.gmt # load GMTDataArray accessor information

   .

Let me know if you need any help. I'm happy to push some changes directly to this branch too if you're ok with working on this together.

[maxrjones]

Thanks for the ping @weiji14. I will prioritize this PR tomorrow (8/31) or am fine with you pushing changes if you post a message first.

[maxrjones]

@weiji14, thanks for your detailed comment. I named the function load_dataarray rather than load_datagrid to be more specific about the output type. Of course, you can comment if you disagree with this decision.

[seisman]

Looks a clean solution to me!

[weiji14]

@weiji14, thanks for your detailed comment. I named the function load_dataarray rather than load_datagrid to be more specific about the output type. Of course, you can comment if you disagree with this decision.

Ok with renaming this to load_dataarray. It's not a commonly used function I think, so hopefully the xarray folks don't mind 😸 Other than that, only a few more minor suggestions on the docstrings.

[maxrjones]

I would prefer to wait to merge this until after #1458 so that I can resolve the merge conflict rather than causing one for that PR.