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Merge pull request #3776 from alphagov/utils-polygons

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Replace polygons module with the one from utils
This commit is contained in:
Chris Hill-Scott
2021-02-12 15:08:46 +00:00
committed by GitHub
parent f83a8b49f1 769b85ff25
commit 691e1396f3
4 changed files with 3 additions and 189 deletions
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2
app/broadcast_areas/__init__.py
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@@ -1,8 +1,8 @@
from notifications_utils.formatters import formatted_list
from notifications_utils.polygons import Polygons
from notifications_utils.serialised_model import SerialisedModelCollection
from werkzeug.utils import cached_property
from .polygons import Polygons
from .populations import CITY_OF_LONDON
from .repo import BroadcastAreasRepository

2
app/broadcast_areas/create-broadcast-areas-db.py
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@@ -6,8 +6,8 @@ from pathlib import Path
import geojson
from notifications_utils.formatters import formatted_list
from notifications_utils.polygons import Polygons
from polygons import Polygons
from populations import (
BRYHER,
CITY_OF_LONDON,

186
app/broadcast_areas/polygons.py
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@@ -1,186 +0,0 @@
import itertools
from shapely.geometry import (
JOIN_STYLE,
GeometryCollection,
MultiPolygon,
Polygon,
)
from shapely.ops import unary_union
from werkzeug.utils import cached_property
class Polygons():
approx_metres_to_degree = 111_320
approx_square_metres_to_square_degree = approx_metres_to_degree ** 2
square_degrees_to_square_miles = (
approx_square_metres_to_square_degree / (1000 * 1000) * 0.386102
)
# Estimated amount of bleed into neigbouring areas based on typical
# range/separation of cell towers.
approx_bleed_in_degrees = 1_500 / approx_metres_to_degree
# Controls how much buffer to add for a shape of a given perimeter.
# Smaller number means more buffering and a smoother shape. For
# example `1000` means 1m of buffer for every 1km of perimeter, or
# 20m of buffer for a 5km square. This gives us control over how
# much we fill in very concave features like channels, harbours and
# zawns.
perimeter_to_buffer_ratio = 360
# Ratio of how much detail a shape of a given perimeter has once
# simplified. Smaller number means less detail. For example `1000`
# means that for a shape with a perimeter of 1000m, the simplified
# line will never deviate more than 1m from the original.
# Or for a 5km square, the line won’t deviate more than 20m. This
# gives us approximate control over the total number of points.
perimeter_to_simplification_ratio = 1_620
# The threshold for removing very small areas from the map. These
# areas are likely glitches in the data where the shoreline hasn’t
# been subtracted from the land properly
minimum_area_size_square_metres = 6_500
def __init__(self, polygons):
if not polygons:
self.polygons = []
elif isinstance(polygons[0], list):
self.polygons = [
Polygon(polygon) for polygon in polygons
]
else:
self.polygons = polygons
def __getitem__(self, index):
return self.polygons[index]
def __len__(self):
return len(self.polygons)
@cached_property
def perimeter_length(self):
return sum(
polygon.length for polygon in self
)
@cached_property
def buffer_outward_in_degrees(self):
return (
# If two areas are close enough that the distance between
# them is less than the minimum bleed of a cell
# broadcast then this joins them together. The aim is to
# reduce the total number of polygons in areas with many
# small shapes like Orkney or the Isles of Scilly.
self.approx_bleed_in_degrees / 3
) + (
self.perimeter_length / self.perimeter_to_buffer_ratio
)
@cached_property
def buffer_inward_in_degrees(self):
return self.buffer_outward_in_degrees - (
# We should leave the shape expanded by at least the
# simplification tolerance in all places, so the
# simplification never moves a point inside the original
# shape. In practice half of the tolerance is enough to
# acheive this.
self.simplification_tolerance_in_degrees / 2
)
@cached_property
def simplification_tolerance_in_degrees(self):
return self.perimeter_length / self.perimeter_to_simplification_ratio
@cached_property
def smooth(self):
buffered = [
polygon.buffer(
self.buffer_outward_in_degrees,
resolution=4,
join_style=JOIN_STYLE.round,
)
for polygon in self
]
unioned = union_polygons(buffered)
debuffered = [
polygon.buffer(
-1 * self.buffer_inward_in_degrees,
resolution=1,
join_style=JOIN_STYLE.bevel,
)
for polygon in unioned
]
flattened = list(itertools.chain(*[
flatten_polygons(polygon) for polygon in debuffered
]))
return Polygons(flattened)
@cached_property
def simplify(self):
return Polygons([
polygon.simplify(self.simplification_tolerance_in_degrees)
for polygon in self
])
@cached_property
def bleed(self):
return Polygons(union_polygons([
polygon.buffer(
self.approx_bleed_in_degrees,
resolution=4,
join_style=JOIN_STYLE.round,
)
for polygon in self
]))
@cached_property
def remove_too_small(self):
return Polygons([
polygon for polygon in self
if (
polygon.area * self.approx_square_metres_to_square_degree
) > (
self.minimum_area_size_square_metres
)
])
@cached_property
def as_coordinate_pairs_long_lat(self):
return [
[[x, y] for x, y in polygon.exterior.coords]
for polygon in self
]
@cached_property
def as_coordinate_pairs_lat_long(self):
return [
[[y, x] for x, y in coordinate_pairs]
for coordinate_pairs in self.as_coordinate_pairs_long_lat
]
@cached_property
def point_count(self):
return len(list(itertools.chain(*self.as_coordinate_pairs_long_lat)))
@property
def estimated_area(self):
return sum(
polygon.area for polygon in self
) * self.square_degrees_to_square_miles
def flatten_polygons(polygons):
if isinstance(polygons, GeometryCollection):
return []
if isinstance(polygons, MultiPolygon):
return [
p for p in polygons
]
else:
return [polygons]
def union_polygons(polygons):
return flatten_polygons(unary_union(polygons))

2
app/models/broadcast_message.py
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@@ -1,12 +1,12 @@
import itertools
from datetime import datetime, timedelta
from notifications_utils.polygons import Polygons
from notifications_utils.template import BroadcastPreviewTemplate
from orderedset import OrderedSet
from werkzeug.utils import cached_property
from app.broadcast_areas import CustomBroadcastAreas, broadcast_area_libraries
from app.broadcast_areas.polygons import Polygons
from app.formatters import round_to_significant_figures
from app.models import JSONModel, ModelList
from app.models.user import User