Plot colored polygons with geodataframe in folium

Question

I'm trying to plot radar data in folium, and I'm almost there. I followed this example (Contour plot data (lat,lon,value) within boundaries and export GeoJSON) to get my data into a GeoJson format.

nb_class = 20 
collec_poly = plt.contourf(lons,lats,np.array(poshdata), nb_class,alpha=0.5)

gdf = collec_to_gdf(collec_poly) # From link above
gdf.to_json()
colors = [p.get_facecolor().tolist()[0] for p in collec_poly.collections]
gdf['RGBA'] = colors

gdf

This outputs two columns: geometry and RGBA.

    RGBA    geometry
0   [0.0, 0.0, 0.713903743316, 1.0] (POLYGON ((-71.57032079644679 42.2775236331535...
1   [0.0, 0.0960784313725, 1.0, 1.0]    (POLYGON ((-71.56719970703125 42.2721176147460...
2   [0.0, 0.503921568627, 1.0, 1.0] (POLYGON ((-71.55678558349609 42.2721176147460...
3   [0.0, 0.896078431373, 0.970904490829, 1.0]  (POLYGON ((-71.52552795410156 42.2849182620049...
4   [0.325743200506, 1.0, 0.641998734978, 1.0]  (POLYGON ((-71.49427795410156 42.2939676156927...
5   [0.641998734978, 1.0, 0.325743200506, 1.0]  (POLYGON ((-71.47344207763672 42.3003084448852...
6   [0.970904490829, 0.959331880901, 0.0, 1.0]  (POLYGON ((-71.26508331298828 42.3200411822557...
7   [1.0, 0.581699346405, 0.0, 1.0] (POLYGON ((-71.15048217773438 42.3333218460720...

From there I make my folium map:

import folium    

# Picked location between Sudbury and Somerville:
maploc = folium.Map(location=[42.377157,-71.236088],zoom_start=11,tiles="Stamen Toner")

folium.GeoJson(gdf).add_to(maploc)

This creates my nice folium map, but the polygons are not colored at all. How do I get the contours to be filled with the right colors? And fix the opacity?

Answer 1

I think I figured it out. In my previous code, polygon.get_facecolor() returns a list of RGBA values ranging from 0-1. I added this function (modified from this post):

def convert_to_hex(rgba_color) :
    red = str(hex(int(rgba_color[0]*255)))[2:].capitalize()
    green = str(hex(int(rgba_color[1]*255)))[2:].capitalize()
    blue = str(hex(int(rgba_color[2]*255)))[2:].capitalize()

    if blue=='0':
        blue = '00'
    if red=='0':
        red = '00'
    if green=='0':
        green='00'

    return '#'+ red + green + blue

to convert it to a hex string. Then:

gdf['RGBA'] = convert_to_hex(colors)

Then to plot the colors in folium, I do:

maploc = folium.Map(location=[42.377157,-71.236088],zoom_start=10,tiles="Stamen Toner")

colors = []
folium.GeoJson(
    gdf,
    style_function=lambda feature: {
        'fillColor': feature['properties']['RGBA'],
        'color' : feature['properties']['RGBA'],
        'weight' : 1,
        'fillOpacity' : 0.5,
        }
    ).add_to(maploc)

and that created a really nice looking plot! (The property name is a bit misleading - it's not actually RGBA values, but hex strings.)