用圆角坐标在 Python 中序列化 GeoJSON答案

【问题标题】：Serialize GeoJSON in Python with rounded coordinates用圆角坐标在 Python 中序列化 GeoJSON
【发布时间】：2020-07-30 18:16:50
【问题描述】：

我想在 Python 中以有限的坐标精度序列化 GeoJSON FeatureCollections。

例如，这是一个 FeatureCollection（在 Python 中表示为 dicts 和 lists）：

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "name": "Liberty Island",
        "area_sqm": 24950.40123456,
        "established": 1875,
        "height_ft": 305
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [ -74.04715418815613, 40.690994683044906 ],
            [ -74.04499769210815, 40.68873311507798 ],
            [ -74.04354929924011, 40.689676800252016 ],
            [ -74.04715418815613, 40.690994683044906 ]
          ]
        ]
      }
    }
  ]
}

我可以使用json.dumps对其进行序列化：

print(json.dumps(fc))

这会打印出 JSON：

{"type": "FeatureCollection", "features": [{"type": "Feature", "properties": {"name": "Liberty Island", "area_sqm": 24950.40123456, "established": 1875, "height_ft": 305}, "geometry": {"type": "Polygon", "coordinates": [[[-74.04715418815613, 40.690994683044906], [-74.04499769210815, 40.68873311507798], [-74.04354929924011, 40.689676800252016], [-74.04715418815613, 40.690994683044906]]]}}]}

那些坐标太精确了。根据 Wikipedia 的说法，7 digits is ~cm precision 应该已经足够好了。我得到的是~纳米精度。

我想序列化 GeoJSON FeatureCollection，坐标只有七位精度。请注意，我想对 properties 中的所有内容使用 Python 的默认序列化：因为这些值可能是任何东西，所以我不能就多少精度就足够了。

我想要的输出是这样的：

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "name": "Liberty Island",
        "area_sqm": 24950.40123456,
        "established": 1875,
        "height_ft": 305
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [ -74.0471541, 40.6909946 ],
            [ -74.0449976, 40.6887331 ],
            [ -74.0435492, 40.6896768 ],
            [ -74.0471541, 40.6909946 ]
          ]
        ]
      }
    }
  ]
}

【问题讨论】：

标签： python json python-3.x geojson

【解决方案1】：

我不确定您所追求的确切序列化，但是当涉及到FeatureCollection 简化时，这应该可以帮助您入门：

import json
from copy import copy


def simplify_geometries(feat_collection):
    new_coll = copy(feat_collection)
    old_features = new_coll['features']
    new_features = []

    for feature in old_features:
        geometry = feature['geometry']
        coords = shorten_arr(geometry['coordinates'])
        geometry['coordinates'] = coords

        new_features.append(feature)

    new_coll['features'] = new_features
    return json.dumps(new_coll)


print(simplify_geometries(
    json.loads('{"type": "FeatureCollection",...')
))

shorten_arr 是一个简单的递归：

def shorten_arr(arr, dec_places=7):
    if not isinstance(arr, list):
        return round(arr, dec_places)

    to_ret = []
    for n in arr:
        if isinstance(n, list):
            n = shorten_arr(n, dec_places)
        to_ret.append(shorten_arr(n, dec_places))
    return to_ret

【讨论】：

这个@danvk运气好吗？