def polygonize(self, band_number=1):
"""
Extract shapes from raster features. This is the inverse operation of rasterizing shapes.
Uses the `Rasterio <https://mapbox.github.io/rasterio/_modules/rasterio/features.html>'_ library
for this purpose. The data is loaded into a `geopandas <http://geopandas.org/user.html>`_ GeoDataFrame.
GeoDataFrame data structures are pandas DataFrames with added functionality, containing a ``geometry``
column for the `Shapely <http://toblerity.org/shapely/shapely.geometry.html>`_ geometries.
The raster data should be loaded in the layer before calling this method.
:param int band_number: The index of the raster band which is to be used as input for extracting \
gemetrical shapes.
:returns: geopandas.GeoDataFrame
"""
raster_data = self.read(band_number)
mask = raster_data != self.raster_reader.nodata
T0 = self.raster_reader.affine
shapes = features.shapes(raster_data, mask=mask, transform=T0)
df = GeoDataFrame.from_records(shapes, columns=['geometry', 'value'])
# convert the geometry dictionary from a dictionary format like {'coordinates': [[(-73.5, 83.5),
# (-73.5, 83.0),
# (-68.0, 83.0),
# (-68.0, 83.5),
# (-73.5, 83.5)]],
# 'type': 'Polygon'}
# to a proper shapely polygon format
df.geometry = df.geometry.apply(lambda row: Polygon(row['coordinates'][0]))
df.crs = self.raster_reader.crs
return df
def intersections(sources, targets, area_cutoff=None):
"""Computes all of the nonempty intersections between two sets of geometries.
The returned `~geopandas.GeoSeries` will have a MultiIndex, where the geometry
at index *(i, j)* is the intersection of ``sources[i]`` and ``targets[j]``
(if it is not empty).
:param sources: geometries
:type sources: :class:`~geopandas.GeoSeries` or :class:`~geopandas.GeoDataFrame`
:param targets: geometries
:type targets: :class:`~geopandas.GeoSeries` or :class:`~geopandas.GeoDataFrame`
:rtype: :class:`~geopandas.GeoSeries`
:param area_cutoff: (optional) if provided, only return intersections with
area greater than ``area_cutoff``
:type area_cutoff: Number or None
"""
reindexed_sources = get_geometries_with_range_index(sources)
reindexed_targets = get_geometries_with_range_index(targets)
spatially_indexed_sources = IndexedGeometries(reindexed_sources)
records = [
# Flip i, j to j, i so that the index is ["source", "target"]
(sources.index[j], targets.index[i], geometry) for i, j, geometry in
spatially_indexed_sources.enumerate_intersections(reindexed_targets)
]
df = GeoDataFrame.from_records(records,
columns=["source", "target", "geometry"])
geometries = df.set_index(["source", "target"]).geometry
geometries.sort_index(inplace=True)
geometries.crs = sources.crs
if area_cutoff is not None:
geometries = geometries[geometries.area > area_cutoff]
return geometries
