folium 图中的非线性色彩图

Question

我正在使用对数比例阴影在

folium

地图上绘制彩色区域。使用自定义颜色图，区域颜色似乎没问题。但是，当将颜色图添加到地图图例时，它看起来仍然是线性的：

有没有办法将其绘制为等宽的彩色矩形，下面有文本值？

import numpy as np, branca, folium
m = folium.Map()
colormap = branca.colormap.LinearColormap(colors=['blue', 'green', 'yellow', 'orange', 'red'],
                                          index = np.round(np.exp(np.linspace(0, 9, 5))),
                                          vmin = 0, vmax = np.exp(9),
           ).to_step(n=6, index=np.round(np.exp(np.linspace(0, 9, 6))))
colormap.add_to(m)

Answer 1

Folium 没有原生方法可以做到这一点，而且布兰卡图例似乎无法自定义缩放。我发现的解决方法是单独创建图例（我使用 matplotlib），然后将其作为自定义图标覆盖在 Folium 地图上。看起来像这样：

import matplotlib.pyplot as plt
import matplotlib.lines as mlines
import numpy as np
import folium
from folium.features import CustomIcon
import matplotlib.colors as mcolors

def generate_legend(num_colors):
    # dynamically generate a color map
    cmap = plt.get_cmap('viridis', num_colors)
    colors = [cmap(i) for i in range(cmap.N)]
    
    # generate labels based on how many colors there are
    log_labels = np.logspace(0, num_colors, num=num_colors, base=10).astype(int)
    
    fig, ax = plt.subplots(figsize=(6, 0.6))
    font_size = 12
    line_width = 30 
    
    # create colors
    for i, color in enumerate(colors):
        plt.plot([i, i+1], [1, 1], color=color, solid_capstyle='butt', linewidth=line_width)
        plt.text(i+0.5, 0.5, f'{log_labels[i]}', ha='center', va='center', fontsize=font_size, transform=ax.transData)

    ax.set_xlim(0, num_colors)
    ax.set_ylim(0, 2)
    ax.axis('off')
    plt.subplots_adjust(left=0, right=1, top=1, bottom=0, wspace=0, hspace=0)
    plt.savefig('dynamic_legend.png', dpi=300, transparent=True, bbox_inches='tight', pad_inches=0)
    plt.close()

    # add legend to map
    m = folium.Map(location=[20, 0], zoom_start=2)
    legend_img = 'dynamic_legend.png'
    icon = CustomIcon(legend_img, icon_size=(600, 120))  # Adjust icon size as needed

    marker = folium.Marker(location=[-25, 0], icon=icon, popup='Legend')  # Adjust location as needed
    m.add_child(marker)

    m.save('map_with_dynamic_legend.html')

num_colors = 5  
generate_legend(num_colors)