Bug plotting polygon of logical children of polygons

[ajfriend]

import h3

def logical_poly(cell, res):
    """
    Return the polygon representing the geometric area covered
    by the children of `cell` at resolution `res`.

    Expectation: A single polygon with one outer loop and no holes.
    Currently: Getting multipolygons with holes (seems like a bug), or just errors for malformed polygons.
    """
    kids = h3.cell_to_children(cell, res)
    mpoly = h3.cells_to_h3shape(kids, tight=False)
    return mpoly

Demonstrated here: https://gist.github.com/ajfriend/dc33458c7cc0e0be88fbc8cee205ce6f

• Generally, we only see the problem of getting multipolygons with odd resolutions.
• However, we also get errors on res 2 and 7 from malformed polygons.

[ajfriend]

This may have been fixed in v4.1 of the core library.

[ajfriend]

Seeing issue in {'c': '4.0.0', 'python': '4.0.0b7'}

[ajfriend]

Bumping to v4.1 we fix all the resolutions >=3, but we get malformed polygons at resolutions 1 and 2.

For example:

h3.cell_to_children('80ebfffffffffff', 1)
['81ea3ffffffffff',
 '81eabffffffffff',
 '81eafffffffffff',
 '81eb3ffffffffff',
 '81eb7ffffffffff',
 '81ebbffffffffff']

[ajfriend]

Should be this bug: uber/h3#917

[ajfriend]

Everything works in v4.1 except for resolutions 1 and 2: https://gist.github.com/ajfriend/5594157463b88eb8d4cae35705657d8d