Enable GeoPandas drawing

[BibMartin]

Addresses #34.

Note that it only works with GeoDataFrame, because GeoSeries.to_json method fails (it's inherited from pandas.Series and does not link to the feature transformation code).

As for example notebook, the link is here :
http://nbviewer.ipython.org/github/bibmartin/folium/blob/geopandas/examples/GeoPandas.ipynb

[ocefpaf]

Let's use isinstance I have a few custom object with to_crs() defined 😉
Also, if we use geopandas.geodataframe.GeoDataFrame we can probably drop the next if below.

[BibMartin]

My goal was to avoid importing geopandas explicitely in folium.
Otherwise, we'll have another dependency.

Maybe there's some other way to filter that.

'geopandas' in data.__class__().__str__()

is ugly, but may work.

[ocefpaf]

Don't know what would be the best approach 😑

Sometimes I think that empowering users by showing how to convert a GeoDataFrame to GeoJSON, and its pyproj like crs to EPSG would be better than wrapping all that in folium...

[ocefpaf]

How about we do something like this:

if/elif(s) and at the else:

else:
    from geopandas import GeoDataFrame, GeoSeries
    self.embed = True
    if isinstance(data, GeoDataFrame):
        self.data = json.loads(data.to_crs(epsg='4326').to_json())
    elif isinstance(data, GeoSeries):
        self.data = json.loads(data.__geo_interface__)
    else:
        raise ValueError('Unhandled data type {!r}.'.format(data))

This is untested, but I prefer this patter because the ImportError has the information we need and the code reads better (IMO 😉).

If you disagree let's at least put the {!r} when raising the ValueError. That might help people to debug what object triggered the problem.

[BibMartin]

@ocefpaf
If I try to pass an unappropriate object to GeoJson, I shall get

ValueError('Unhandled data type {!r}.'.format(data))

Yet with your piece of code, if I have not installed geopandas, I will get

ImportError

Well, this is a matter of readability ; I'll try to think to it further in the coming days.

[ocefpaf]

@BibMartin you are right. My way can hinder some other failure unrelated to the optional dependency.

However, one might argue that whatever we supported was already tested. An alternative would be to use a try/except ImportError and re-raise it with a new message. "Need optional dependecy geopandas. Could not parse object {!r}."

Anyway, this is not crucial to this PR. I guess that the main goal is to avoid the need of Geopandas as a core dependency. If that starts to get in the way we might try to make this external in a different way. Not sure how yet. I trust your judgement here. Just let me know when you are OK with this so I can merge it.

[BibMartin]

@ocefpaf
Thanks to geopandas/geopandas#262, I've realized that geopandas objects now have a __geo_interface__ attribute that does (almost) all the job.
So here is another suggestion to handle the pb...

Please tell me if you're okay with this ; I'll squash commits then.

[ocefpaf]

The self.embed = True and data.to_crs(epsg='4326') could be up one level to avoid repetition.

PS: __geo_interface__ is a dict, right? Just making sure that we need the json.dumps.

[BibMartin]

The self.embed = True could be up one level to avoid repetition

True. I do it.

data.to_crs(epsg='4326') could be up one level to avoid repetition

No, otherwise, the Exception 'Unable to transform this object to a GeoJSON.' will be replaced by Unknown method 'to_crs' (or something like this).

PS: geo_interface is a dict, right? Just making sure that we need the json.dumps.

__geo_interface__ is a dict. But we need to do a deep copy of the object here ; otherwise, we'll have unintended side effects : further folium computation (like styling) may modify the geopandas object...

[ocefpaf]

No, otherwise, the Exception 'Unable to transform this object to a GeoJSON.' will be replaced by Unknown method 'to_crs' (or something like this).

I was thinking of a copy like:

a = data.to_crs(epsg='4326')

and then

a.__geo_interface__ or a.to_json()

But that way is fine.

[ocefpaf]

Some minor comments. Will merge as soon as you ping me back.

[BibMartin]

@ocefpaf
Thanks for your feedback.

Answers are in the code.

Squashed and ready for merge if all is ok to you.

[ocefpaf]

Awesome @BibMartin!

I always learn a lot by reviewing your PRs. Thanks!