Handle geopandas and shapely geometries via geo_interface link

[weiji14]

Description of proposed changes

Enabling PyGMT to use GeoPandas data structures! This includes plotting geopandas.GeoDataFrame tables and running data processing tasks. Works by converting the GeoJSON __geo_interface__ representation to an OGR_GMT file format and passing that into GMT.

Preview API doc example at https://pygmt-git-geopandasintegration-gmt.vercel.app/api/generated/pygmt.info.html.

Example code (note that the should work directly in PyGMT v0.4.0 since #1000 is merged!):

import geopandas as gpd
import pygmt
import shapely.geometry

# Create a geopandas GeoDataFrame
gdf = gpd.GeoDataFrame(
    geometry=[shapely.geometry.Polygon([(20, 10), (23, 10), (23, 14), (20, 10)])],
)

pygmt.info(table=gdf, per_column=True)
# array([20., 23., 10., 14.])

References:

• https://gist.github.com/sgillies/2217756
• https://github.com/mlaloux/Python-geo_interface-applications

TODO:

• Handle geopandas.GeoDataFrame via gpd.to_file
• Handle shapely.geometry (not very satisfactory as it still depends on having geopandas installed, would prefer a pure fiona solution)
• Add tests for plotting via fig.plot(data=gdf) works (will do after Refactor plot and plot3d to use virtualfile_from_data #990)
• etc

Fixes #608

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

[weiji14]

This was my failed attempt to convert a GeoJSON string to an OGR_GMT (*.gmt) format file purely using fiona (i.e. no geopandas installed). The problem I found was that a schema had to be set, and that requires a lot of lines of code to do, which is why I stuck to using geopandas in the lines above.

If someone can figure out a good way to solve the schema problem, that would be fantastic!

[weiji14]

Ok, I've removed this chunk of unusable code in 34de789. Hopefully this can be revisited in the future so that GeoJSON objects can be converted into OGR_GMT purely using fiona without the need for installing geopandas (a bit of a big dependency).

[seisman]

What's the reason for this?

[weiji14]

Since geopandas is an optional dependency, probably good to have a test matrix that doesn't include it.

[seisman]

Looks great.

[weiji14]

Checking with @michaelgrund if you have any other comments on this geopandas integration PR? If not, I'll merge in the next 24 hours.