#!/usr/bin/env python
# coding: utf-8

# In[1]:


import os
import folium

print(folium.__version__)


# # Illustration of CRS effect
# 
# Leaflet is able to handle several CRS (coordinate reference systems). It means that depending on the data you have, you may need to use the one or the other.
# 
# Don't worry ; in practice, almost everyone on the web uses EPSG3857 (the default value for folium and Leaflet). But it may be interesting to know the possible values.
# 
# Let's create a GeoJSON map, and change it's CRS.

# In[2]:


import json

us_states = os.path.join('data', 'us-states.json')

geo_json_data = json.load(open(us_states))


# ## EPSG3857 ; the standard
# 
# Provided that our tiles are computed with this projection, this map has the expected behavior.

# In[3]:


kw = dict(tiles=None, location=[43, -100], zoom_start=3)


# In[4]:


m = folium.Map(crs='EPSG3857', **kw)

folium.GeoJson(geo_json_data).add_to(m)

m.save(os.path.join('results', 'CRS_0.html'))

m


# ## EPSG4326
# 
# This projection is a *common CRS among GIS enthusiasts* according to Leaflet's documentation. And we see it's quite different.

# In[5]:


m = folium.Map(crs='EPSG4326', **kw)

folium.GeoJson(geo_json_data).add_to(m)

m.save(os.path.join('results', 'CRS_1.html'))

m


# ## EPSG3395
# 
# The elliptical projection is almost equal to EPSG3857 ; though different.

# In[6]:


m = folium.Map(crs='EPSG3395', **kw)

folium.GeoJson(geo_json_data).add_to(m)

m.save(os.path.join('results', 'CRS_2.html'))

m


# ## Simple
# 
# At last, Leaflet also give the possibility to use no projection at all. With this, you get flat charts.
# 
# It can be useful if you want to use folium to draw non-geographical data.

# In[7]:


m = folium.Map(crs='Simple', **kw)

folium.GeoJson(geo_json_data).add_to(m)

m.save(os.path.join('results', 'CRS_3.html'))

m