未定义 geodataframe

Question

我正在使用Jupiter、ipywidgets和Ipyleaflet，试图在地图上绘制多边形并保存到一个地理数据框中。在我的笔记本单元格里有以下内容：

zoom = 15

from ipywidgets import Output, interact
import ipywidgets
from __future__ import print_function
import ipyleaflet
import geopandas as gpd
import pandas as pd

# from shapely.geometry import Point, LineString, Polygon
from shapely import geometry


from ipyleaflet import (
    Map,
    Marker,
    TileLayer, ImageOverlay,
    Polyline, Polygon, Rectangle, Circle, CircleMarker,
    GeoJSON,
    DrawControl)

# Create an Output widget
out = Output()

# Define a function to handle interactions
def handle_interaction(change):
    with out:
        print(change)


c = ipywidgets.Box()
c.children = [m]

# keep track of rectangles and polygons drawn on map:
def clear_m():
    global rects,polys
    rects = set()
    polys = set()

clear_m()
rect_color = '#a52a2a'
poly_color = '#00F'

myDrawControl = DrawControl(
rectangle={'shapeOptions':{'color':rect_color}},
        polygon={'shapeOptions':{'color':poly_color}}) #,polyline=None)

def handle_draw(self, action, geo_json):
    global rects,polys
    polygon=[]
    for coords in geo_json['geometry']['coordinates'][0][:-1][:]:
        handle_interaction(coords)
        polygon.append(tuple(coords))
    polygon = tuple(polygon)
    handle_interaction(polygon)
    if geo_json['properties']['style']['color'] == '#00F':  # poly
        if action == 'created':
            handle_interaction(" in here")
            polys.add(polygon)
            polygon_geom = geometry.Polygon(polygon)
    
            # Create GeoDataFrame if it doesn't exist
            if gdf2: is None:
                gdf2 = gpd.GeoDataFrame(geometry=[polygon_geom])
            else:
                gdf2 = gdf2.append({'geometry': polygon_geom}, ignore_index=True)
            
        elif action == 'deleted':
            polys.discard(polygon)
    if geo_json['properties']['style']['color'] == '#a52a2a':  # rect
        if action == 'created':
            rects.add(polygon)
        elif action == 'deleted':
            rects.discard(polygon)
myDrawControl.on_draw(handle_draw)
m.add_control(myDrawControl)

在地图上绘制形状后，我可以看到

display(out)

[-88.434269, 31.660818] [-88.431051, 31.661439] [-88.431265, 31.660087] [-88.433582, 31.659941] ((-88.434269, 31.660818), (-88.431051, 31.661439), (-88.431265, 31.660087), (-88.433582, 31.659941)) 在这里 [-88.432166, 31.658474] [-88.429678, 31.65767] [-88.431609, 31.656684] [-88.434054, 31.65778] ((-88.432166, 31.658474), (-88.429678, 31.65767), (-88.431609, 31.656684), (-88.434054, 31.65778)) 在这里

这些是在下一个单元格中列出的（预期的结果）。但是当我尝试：

print(gdf2)

我得到了：

NameError: name 'gdf2' is not defined

我哪里做错了？

Answer 1

我不太确定你是不是没有粘贴完整的代码，不过除了你函数内部的局部环境之外，确实没有地方定义过 gdf2。gdf2 需要是一个全局变量。

Answer 2

gdf2是handle_draw函数里的一个局部变量。这意味着它在这个函数外面是无法使用的。

如果你想保留它的值，可以在函数外面先定义它，比如：

zoom = 15
gdf2 = None 

然后在handle_draw函数的开头使用global关键字：

def handle_draw(self, action, geo_json):
    global gdf2 

注意：已经编辑过，只保留了答案部分