Addition of new functionalities for formatting the Cartopy.gridliner ticklabels

[PhilipeRLeal]

Dear all,

I would like to make a pull request in cartopy in order to add a new set of functionalities for cartopy's gridline.

The new functionalities encompass small functions that allow any given user to easily format the gridline ticklabel settings (i.e.: decimal separator symbol, hemisphere symbology, etc.).

Rationale

These new assets have been derived from my personal struggle with cartopy's geoaxes and the continuous migration from the past basemap towards cartopy.

In this new branch, the geoaxes class has gained new assets for ticklabel formatting.

This background of this pull request is presented in a comment from the stackoverflow (see here). At the current time, cartopy only supports a fixed set of geographical units for the xticklabels and yticklabels (i.e.: "W" for west coordinates, "E" for east coordinates, "S" for south coordinates, "N" for north coordinates), with no easy way to change them to a user's defined version. Also, there is no easy way to convert the decimal symbol of the coordinates (i.e.: dot "."). For users like me who come from Latin countries, there is a great demand for latin symbols, therefore, instead of using [W,E,S,N and dot"."], one should use the following respectively [O, L, S, N and ","].

Here is a relation of the provided symbols:

O (from Oeste) == West
L (from Leste) == East
N (from Norte) == North
S (from Sul) == South
'.' == ','

I state here that all prior symbols [W,E,S,N and dot"."] have been kept as they were (in international format). Therefore, no changes have been made to the common cartopy's gridline usage. This new Pull request only allows the user to easily change those symbols into any user's defined string/symbol.

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The list of the new functionalities related to gridline ticklabel settings:

1. addition of a method for easy setting the decimal separators from the gridline ticklabels (i.e.: dot '.' to comma ',')
2. addition of a method for easy setting the maximum number of ticks in the gridline
3. addition of a method for easy setting the hemispheric labels (i.e.: 'N', 'S', 'W' and 'E') to any other provided strings (i.e.: 'Norte', 'Sul', 'Leste', 'Oeste')

Observation:

This is a subdivision of the prior pull request #1693.

In accordance to GregLucas, the former pull request was subdivided into small ones, being this respective pull request solely regarding the gridline ticklabel settings

Check pull request #1698 for the scalebar asset.

Usage example:

import cartopy.crs as ccrs
import cartopy.feature as cfeature

import matplotlib.pyplot as plt


def main():

    plt.figure(figsize=(7, 3))
    ax = plt.axes(projection=ccrs.PlateCarree())
    ax.set_extent([-65, -40, -15, 10])

    # Create a feature for States/Admin 1 regions at 1:50m from Natural Earth
    states_provinces = cfeature.NaturalEarthFeature(
        category='cultural',
        name='admin_1_states_provinces_lines',
        scale='50m',
        facecolor='none')
    ax.add_feature(states_provinces, edgecolor='gray')

    ax.coastlines(resolution='110m')
    ax.coastlines(resolution='110m')
    gl = ax.gridlines(draw_labels=True)

    gl.change_gridline_tick_decimal_separator('{0:.3f}',
                                              axis='both')

    gl.set_latitude_hemisphere_str('Norte', 'Sul')

    gl.set_longitude_hemisphere_str('O', 'L')

    gl.top_labels = False
    gl.right_labels = False
    plt.show()

    return plt.gcf().get_axes(), gl

Implications

None

[PhilipeRLeal]

Dear all,

I am wondering when one should close a Pull Request.

In this case, given this pull request (PR) changes, the discussed issue is formally solved. Nevertheless, if this PR is not merged into the main branch of cartopy (i.e.: in the next cartopy's release), the issue will remain present.

I thank you for your time,