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feat: add enclose_poles to antimeridian module
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@gadomski
gadomski committed Apr 10, 2023
1 parent d5c3f35 commit 3624c91
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Showing 2 changed files with 199 additions and 15 deletions.
116 changes: 115 additions & 1 deletion src/stactools/core/utils/antimeridian.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,11 @@
"""`Antimeridian <https://en.wikipedia.org/wiki/180th_meridian>`_ utilities."""

from __future__ import annotations

import math
from dataclasses import dataclass
from enum import Enum, auto
from typing import Optional
from typing import List, Optional, Tuple

import shapely.affinity
import shapely.geometry
Expand Down Expand Up @@ -235,3 +239,113 @@ def normalize_multipolygon(multi_polygon: MultiPolygon) -> Optional[MultiPolygon
return MultiPolygon(polygons)
else:
return None


def enclose_poles(polygon: Polygon) -> Polygon:
"""Updates an anti-meridian-crossing polygon to enclose the poles.
This works by detecting anti-meridian crossings and adding points to extend
the geometry up to the north (or down to the south) pole. This is useful for
(e.g.) polar-orbiting satellites who have swaths that go over the poles.
This function will raise a value error if the polygon has any interior rings.
Args:
polygon (:py:class:`shapely.geometry.Polygon`): An input polygon.
Returns:
:py:class:`shapely.geometry.Polygon`: The same polygon, modified to
enclose the poles.
"""
if bool(polygon.interiors):
raise ValueError("cannot enclose poles if there is an interior ring")
coords = list(polygon.exterior.coords)
crossings = list()

# First pass is to detect all antimeridian crossings, without actually
# modifying the coordinates. This is to protect against the case when there
# are additional crossings in between the pole crossings.
for i, (start, end) in enumerate(zip(coords, coords[1:])):
longitude_delta = end[0] - start[0]
if abs(longitude_delta) > 180:
crossings.append(_Crossing.from_points(i, start, end))

# We only want the southernmost and northernmost crossings.
crossings = sorted(crossings, key=lambda c: c.latitude)
if len(crossings) > 2:
crossings = [crossings[0], crossings[-1]]

# If there are two crossings, we know the southernmost one is around the
# south pole and the northernmost is around the north pole, even if the
# crossing latitude is in the other hemisphere.
#
# If we only have one crossing, we just guess that it's crossing on the
# closer pole.
if len(crossings) == 2:
crossings[0].north_pole = False
crossings[1].north_pole = True

# We work from the back of the list so we can use the indices.
crossings = sorted(crossings, key=lambda c: c.index, reverse=True)
for crossing in crossings:
coords = (
coords[0 : crossing.index + 1]
+ crossing.enclosure()
+ coords[crossing.index + 1 :]
)

return Polygon(coords)


@dataclass
class _Crossing:
index: int
latitude: float
positive_to_negative: bool
north_pole: bool

@classmethod
def from_points(
cls, index: int, start: Tuple[float, float], end: Tuple[float, float]
) -> _Crossing:
latitude_delta = end[1] - start[1]
if start[0] > 0:
split_latitude = round(
start[1]
+ (180.0 - start[0]) * latitude_delta / (end[0] + 360.0 - start[0]),
7,
)
return cls(
index=index,
latitude=split_latitude,
positive_to_negative=True,
north_pole=split_latitude > 0,
)
else:
split_latitude = round(
start[1]
+ (start[0] + 180.0) * latitude_delta / (start[0] + 360.0 - end[0]),
7,
)
return cls(
index=index,
latitude=split_latitude,
positive_to_negative=False,
north_pole=split_latitude > 0,
)

def enclosure(self) -> List[Tuple[float, float]]:
if self.positive_to_negative:
longitudes = (180.0, -180.0)
else:
longitudes = (-180.0, 180.0)
if self.north_pole:
pole_latitude = 90.0
else:
pole_latitude = -90.0
return [
(longitudes[0], self.latitude),
(longitudes[0], pole_latitude),
(longitudes[1], pole_latitude),
(longitudes[1], self.latitude),
]
98 changes: 84 additions & 14 deletions tests/core/utils/test_antimeridian.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ def test_antimeridian_split() -> None:
(
shapely.geometry.box(170, 40, 180, 50),
shapely.geometry.box(-180, 40, -170, 50),
)
),
)
for actual, expected in zip(split.geoms, expected.geoms):
assert actual.exterior.is_ccw
Expand All @@ -27,15 +27,15 @@ def test_antimeridian_split() -> None:
assert split is None

canonical_other_way = Polygon(
((-170, 40), (170, 40), (170, 50), (-170, 50), (-170, 40))
((-170, 40), (170, 40), (170, 50), (-170, 50), (-170, 40)),
)
split = antimeridian.split(canonical_other_way)
assert split
expected = MultiPolygon(
(
shapely.geometry.box(-180, 40, -170, 50),
shapely.geometry.box(170, 40, 180, 50),
)
),
)
for actual, expected in zip(split.geoms, expected.geoms):
assert actual.exterior.is_ccw
Expand All @@ -44,7 +44,7 @@ def test_antimeridian_split() -> None:

def test_antimeridian_split_complicated() -> None:
complicated = Polygon(
((170, 40), (170, 50), (-170, 50), (170, 45), (-170, 40), (170, 40))
((170, 40), (170, 50), (-170, 50), (170, 45), (-170, 40), (170, 40)),
)
split = antimeridian.split(complicated)
assert split
Expand All @@ -57,7 +57,7 @@ def test_antimeridian_split_complicated() -> None:
(170.0, 45.0),
(170.0, 40.0),
(180.0, 40.0),
]
],
),
Polygon([(-180.0, 42.5), (-180.0, 40.0), (-170.0, 40.0), (-180.0, 42.5)]),
Polygon(
Expand All @@ -67,10 +67,10 @@ def test_antimeridian_split_complicated() -> None:
(170.0, 50.0),
(170.0, 45.0),
(180.0, 47.5),
]
],
),
Polygon([(-180.0, 50.0), (-180.0, 47.5), (-170.0, 50.0), (-180.0, 50.0)]),
)
),
)
for actual, expected in zip(split.geoms, expected.geoms):
assert actual.exterior.is_ccw
Expand All @@ -86,7 +86,7 @@ def test_antimeridian_normalize() -> None:
assert normalized.equals(expected), f"actual={normalized}, expected={expected}"

canonical_other_way = Polygon(
((-170, 40), (170, 40), (170, 50), (-170, 50), (-170, 40))
((-170, 40), (170, 40), (170, 50), (-170, 50), (-170, 40)),
)
normalized = antimeridian.normalize(canonical_other_way)
assert normalized
Expand Down Expand Up @@ -129,10 +129,11 @@ def test_item_fix_antimeridian_split() -> None:
(
shapely.geometry.box(170, 40, 180, 50),
shapely.geometry.box(-180, 40, -170, 50),
)
),
)
for actual, expected in zip(
shapely.geometry.shape(fix.geometry).geoms, expected.geoms
shapely.geometry.shape(fix.geometry).geoms,
expected.geoms,
):
assert actual.equals(expected)
assert fix.bbox == [170, 40, -170, 50]
Expand All @@ -159,7 +160,7 @@ def test_item_fix_antimeridian_multipolygon_ok() -> None:
(
shapely.geometry.box(170, 40, 180, 50),
shapely.geometry.box(-180, 40, -170, 50),
)
),
)
item = Item(
"an-id",
Expand All @@ -177,7 +178,7 @@ def test_antimeridian_multipolygon() -> None:
[
Polygon(((170, 40), (170, 42), (-170, 42), (-170, 40), (170, 40))),
Polygon(((170, 48), (170, 50), (-170, 50), (-170, 48), (170, 48))),
]
],
)
split = antimeridian.split_multipolygon(multi_polygon)
assert split
Expand All @@ -187,7 +188,7 @@ def test_antimeridian_multipolygon() -> None:
shapely.geometry.box(-180, 40, -170, 42),
shapely.geometry.box(170, 48, 180, 50),
shapely.geometry.box(-180, 48, -170, 50),
)
),
)
for actual, expected in zip(split.geoms, expected.geoms):
assert actual.exterior.is_ccw
Expand All @@ -199,8 +200,77 @@ def test_antimeridian_multipolygon() -> None:
(
Polygon(((170, 40), (170, 42), (190, 42), (190, 40), (170, 40))),
Polygon(((170, 48), (170, 50), (190, 50), (190, 48), (170, 48))),
)
),
)
for actual, expected in zip(normalized.geoms, expected.geoms):
assert actual.exterior.is_ccw
assert actual.equals(expected), f"actual={actual}, expected={expected}"


def test_antimeridian_enclose_poles() -> None:
before = Polygon(((170, 40), (-170, 50), (-170, -50), (170, -40), (170, 40)))
after = antimeridian.enclose_poles(before)
assert after == Polygon(
(
(170, 40),
(180, 45),
(180, 90),
(-180, 90),
(-180, 45),
(-170, 50),
(-170, -50),
(-180, -45),
(-180, -90),
(180, -90),
(180, -45),
(170, -40),
(170, 40),
)
)


def test_antimeridian_enclose_poles_extra_crossing() -> None:
before = Polygon(
((170, 40), (-170, 50), (-170, -50), (170, -40), (-175, 0), (170, 40))
)
after = antimeridian.enclose_poles(before)
assert after == Polygon(
(
(170, 40),
(180, 45),
(180, 90),
(-180, 90),
(-180, 45),
(-170, 50),
(-170, -50),
(-180, -45),
(-180, -90),
(180, -90),
(180, -45),
(170, -40),
(-175, 0),
(170, 40),
)
)


def test_antimeridian_enclose_poles_both_northern_hemisphere() -> None:
before = Polygon(((170, 80), (-170, 80), (-170, 10), (170, 10), (170, 80)))
after = antimeridian.enclose_poles(before)
assert after == Polygon(
(
(170, 80),
(180, 80),
(180, 90),
(-180, 90),
(-180, 80),
(-170, 80),
(-170, 10),
(-180, 10),
(-180, -90),
(180, -90),
(180, 10),
(170, 10),
(170, 80),
)
)

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