GIS：在Python中合并多面体

Question

我在不列颠群岛有geojson file个县，我正试图用一个合并的县代替伦敦的各个县，然后将结果保存为geojson。 （可以识别伦敦县，因为它们的TYPE_2属性设置为London Borough。）

我认为我可以执行以下任务：

from shapely.geometry import Polygon, MultiPolygon, asShape
from shapely.ops import unary_union
import json, geojson

j = json.load(open('british-isles.geojson'))

# find the london counties
indices = [idx for idx, i in enumerate(j['features']) if \
    i['properties']['TYPE_2'] == 'London Borough']

# transform each london county into a shapely polygon
polygons = [asShape(j['features'][i]['geometry']) for i in indices]

# get the metadata for the first county
properties = j['features'][indices[0]]['properties']
properties['NAME_2'] = 'London'

# get the union of the polygons
joined = unary_union(polygons)

# delete the merged counties
d = j
for i in indices:
  del d['features'][i]

# add the new polygon to the features
feature = geojson.Feature(geometry=joined, properties=properties)
d['features'].append(feature)

# save the geojson
with open('geojson-british-isles-merged-london.geojson', 'w') as out:
  json.dump(d, out)

但是，这并不能正确地合并伦敦县-而是导致伦敦县以前的一系列多边形碎片化。

其他人知道我如何在Python中完成此任务吗？任何建议都将非常有帮助！

Answer 1

以上所述有两个问题。第一个纯粹是一个疏忽：从d['features']删除时，我需要以相反的顺序删除数组成员（删除索引0然后1不同于删除1然后0）。

从根本上说，上述geojson已经有损。坐标值的小数位数有限，无法将字节缩减为JSON文件大小。但这使合并的几何形状仅近似，并导致合并的多边形之间的缝隙很小：

因此，我得到的工作流程是获得高分辨率topojson file，将其转换为geojson，使用以下代码合并几何，然后限制十进制精度（如有必要）。 / p>

from shapely.geometry import Polygon, MultiPolygon, asShape
from shapely.ops import unary_union, cascaded_union
from geojson import Feature
import json

j = json.load(open('GBR_adm2.json'))

# find the london counties
indices = [idx for idx, i in enumerate(j['features']) if \
    'London Borough' in i['properties']['TYPE_2']]

# transform each london county into a shapely polygon
polygons = [asShape(j['features'][i]['geometry']) for i in indices]

# get the metadata for the first county
properties = j['features'][indices[0]]['properties']
properties['NAME_2'] = 'London'

# get the union of the polygons
joined = unary_union(polygons)

# delete the merged counties
d = j
for i in reversed(sorted(indices)):
  del d['features'][i]

# add the new polygon to the features
feature = Feature(geometry=joined, properties=properties)
d['features'].append(feature)

# save the geojson
with open('british-isles-merged-london.geojson', 'w') as out:
  json.dump(d, out)

结果：