97 lines
2.7 KiB
Python
97 lines
2.7 KiB
Python
"""This module provides utility functions for integrating with Shapely.
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.. note::
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As GeoAlchemy 2 itself has no dependency on `Shapely`, applications using
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functions of this module have to ensure that `Shapely` is available.
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"""
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from contextlib import contextmanager
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from typing import List
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from typing import Optional
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from typing import Union
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try:
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import shapely.wkb
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import shapely.wkt
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from shapely.wkb import dumps
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HAS_SHAPELY = True
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_shapely_exc = None
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except ImportError as exc:
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HAS_SHAPELY = False
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_shapely_exc = exc
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from geoalchemy2.elements import WKBElement
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from geoalchemy2.elements import WKTElement
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@contextmanager
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def check_shapely():
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if not HAS_SHAPELY:
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raise ImportError(
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"This feature needs the optional Shapely dependency. "
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"Please install it with 'pip install geoalchemy2[shapely]'."
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) from _shapely_exc
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yield
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@check_shapely()
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def to_shape(element: Union[WKBElement, WKTElement]):
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"""Function to convert a :class:`geoalchemy2.types.SpatialElement` to a Shapely geometry.
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Args:
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element: The element to convert into a ``Shapely`` object.
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Example::
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lake = Session.query(Lake).get(1)
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polygon = to_shape(lake.geom)
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"""
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if isinstance(element, WKBElement):
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data, hex = (
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(element.data, True) if isinstance(element.data, str) else (bytes(element.data), False)
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)
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return shapely.wkb.loads(data, hex=hex)
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elif isinstance(element, WKTElement):
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if element.extended:
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return shapely.wkt.loads(element.data.split(";", 1)[1])
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else:
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return shapely.wkt.loads(element.data)
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else:
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raise TypeError("Only WKBElement and WKTElement objects are supported")
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@check_shapely()
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def from_shape(shape, srid: int = -1, extended: Optional[bool] = False) -> WKBElement:
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"""Function to convert a Shapely geometry to a :class:`geoalchemy2.types.WKBElement`.
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Args:
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shape: The shape to convert.
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srid: An integer representing the spatial reference system. E.g. ``4326``.
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Default value is ``-1``, which means no/unknown reference system.
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extended: A boolean to switch between WKB and EWKB.
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Default value is False.
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Example::
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from shapely.geometry import Point
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wkb_element = from_shape(Point(5, 45), srid=4326)
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ewkb_element = from_shape(Point(5, 45), srid=4326, extended=True)
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"""
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return WKBElement(
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memoryview(dumps(shape, srid=srid if extended else None)),
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srid=srid,
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extended=extended,
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)
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__all__: List[str] = [
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"from_shape",
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"to_shape",
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]
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def __dir__() -> List[str]:
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return __all__
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