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geometry.py
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geometry.py
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"""
Helpers for GeoJSON-based geometry objects.
"""
import json
import os
import fiona
import requests
import shapely.geometry
import shapely.ops
def parse_boundary(boundary_file, **kwargs):
"""
Read boundary geometry from a local or remote geojson file.
Parameters:
boundary_file: str
A path to a local file or URL to a remote file with boundary data in geojson format.
output: str, optional
If boundary_file is a URL, download and save the file to this directory.
Return:
shapely.geometry.Polygon
A single unioned Polygon representing the (composite) boundary.
"""
if boundary_file.lower().startswith("http") and boundary_file.lower().endswith(".geojson"):
r = requests.get(boundary_file)
file_name = boundary_file.split("/")[-1]
path = os.path.join(kwargs.get("output", "."), file_name)
with open(path, "w") as f:
json.dump(r.json(), f)
boundary_file = path
# meld all the features together into a unified polygon
features = fiona.open(boundary_file)
polygons = [shapely.geometry.shape(feature["geometry"]) for feature in features]
polygons_meld = shapely.ops.unary_union(polygons)
return shapely.geometry.Polygon(polygons_meld)
def extract_point(feature):
"""
Extract coordinates from a GeoJSON feature.
Parameters:
feature: dict-like
GeoJSON structure with coordinate geometry.
Return:
shapely.geometry.Point
The Point representation of the coordinate geometry.
"""
coords = feature["geometry"]["coordinates"]
return shapely.geometry.Point(coords[0], coords[1])
def to_feature(shape, properties={}):
"""
Create a GeoJSON Feature object from geometry.
Parameters:
shape: shapely.geometry.Shape
The geometry defining this Feature.
properties: dict, optional
Entries for the Feature's properties collection.
Return:
dict
The GeoJSON Feature object.
"""
feature = shapely.geometry.mapping(shape)
feature["properties"] = properties
feature["geometry"] = {}
if isinstance(shape, shapely.geometry.Point):
feature["geometry"]["coordinates"] = list(feature["coordinates"])
else:
# assume shape is polygon (multipolygon will break)
feature["geometry"]["coordinates"] = [list(list(coords) for coords in part) for part in feature["coordinates"]]
# 'type' at the top level is Feature, and in 'geometry' should be set
feature["geometry"]["type"] = feature["type"]
feature["type"] = "Feature"
# 'coordinates' in the top level is not valid geoJSON.
feature.pop("coordinates")
return feature