python - 最近邻加入距离条件
问题描述
在这个问题中,我指的是这个项目:
https://automating-gis-processes.github.io/site/master/notebooks/L3/nearest-neighbor-faster.html
我们有两个 GeoDataFrame:
建筑物:
name geometry
0 None POINT (24.85584 60.20727)
1 Uimastadion POINT (24.93045 60.18882)
2 None POINT (24.95113 60.16994)
3 Hartwall Arena POINT (24.92918 60.20570)
和巴士站:
stop_name stop_lat stop_lon stop_id geometry
0 Ritarihuone 60.169460 24.956670 1010102 POINT (24.95667 60.16946)
1 Kirkkokatu 60.171270 24.956570 1010103 POINT (24.95657 60.17127)
2 Kirkkokatu 60.170293 24.956721 1010104 POINT (24.95672 60.17029)
3 Vironkatu 60.172580 24.956554 1010105 POINT (24.95655 60.17258)
申请后
sklearn.neighbors 导入 BallTree
from sklearn.neighbors import BallTree
import numpy as np
def get_nearest(src_points, candidates, k_neighbors=1):
"""Find nearest neighbors for all source points from a set of candidate points"""
# Create tree from the candidate points
tree = BallTree(candidates, leaf_size=15, metric='haversine')
# Find closest points and distances
distances, indices = tree.query(src_points, k=k_neighbors)
# Transpose to get distances and indices into arrays
distances = distances.transpose()
indices = indices.transpose()
# Get closest indices and distances (i.e. array at index 0)
# note: for the second closest points, you would take index 1, etc.
closest = indices[0]
closest_dist = distances[0]
# Return indices and distances
return (closest, closest_dist)
def nearest_neighbor(left_gdf, right_gdf, return_dist=False):
"""
For each point in left_gdf, find closest point in right GeoDataFrame and return them.
NOTICE: Assumes that the input Points are in WGS84 projection (lat/lon).
"""
left_geom_col = left_gdf.geometry.name
right_geom_col = right_gdf.geometry.name
# Ensure that index in right gdf is formed of sequential numbers
right = right_gdf.copy().reset_index(drop=True)
# Parse coordinates from points and insert them into a numpy array as RADIANS
left_radians = np.array(left_gdf[left_geom_col].apply(lambda geom: (geom.x * np.pi / 180, geom.y * np.pi / 180)).to_list())
right_radians = np.array(right[right_geom_col].apply(lambda geom: (geom.x * np.pi / 180, geom.y * np.pi / 180)).to_list())
# Find the nearest points
# -----------------------
# closest ==> index in right_gdf that corresponds to the closest point
# dist ==> distance between the nearest neighbors (in meters)
closest, dist = get_nearest(src_points=left_radians, candidates=right_radians)
# Return points from right GeoDataFrame that are closest to points in left GeoDataFrame
closest_points = right.loc[closest]
# Ensure that the index corresponds the one in left_gdf
closest_points = closest_points.reset_index(drop=True)
# Add distance if requested
if return_dist:
# Convert to meters from radians
earth_radius = 6371000 # meters
closest_points['distance'] = dist * earth_radius
return closest_points
closest_stops = nearest_neighbor(buildings, stops, return_dist=True)
我们为每个建筑物索引获取到最近的公共汽车站的距离:
stop_name stop_lat stop_lon stop_id geometry distance
0 Muusantori 60.207490 24.857450 1304138 POINT (24.85745 60.20749) 180.521584
1 Eläintarha 60.192490 24.930840 1171120 POINT (24.93084 60.19249) 372.665221
2 Senaatintori 60.169010 24.950460 1020450 POINT (24.95046 60.16901) 119.425777
3 Veturitie 60.206610 24.929680 1174112 POINT (24.92968 60.20661) 106.762619
我正在寻找解决方案,以使每座建筑物的每个公交车站(可能不止一个)的距离都低于 250 米。
谢谢你的帮助。
解决方案
here is a way reusing what has been done with BallTree like in question but with query_radius
instead. Also it is not in function format but you can still change it easily
from sklearn.neighbors import BallTree
import numpy as np
import pandas as pd
## here I start with buildings and stops as loaded in the link provided
# variable in meter you can change
radius_max = 250 # meters
# another parameter, in case you want to do with Mars radius ^^
earth_radius = 6371000 # meters
# similar to the method with apply in the tutorial
# to create left_radians and right_radians, but faster
candidates = np.vstack([stops['geometry'].x.to_numpy(),
stops['geometry'].y.to_numpy()]).T*np.pi/180
src_points = np.vstack([buildings['geometry'].x.to_numpy(),
buildings['geometry'].y.to_numpy()]).T*np.pi/180
# Create tree from the candidate points
tree = BallTree(candidates, leaf_size=15, metric='haversine')
# use query_radius instead
ind_radius, dist_radius = tree.query_radius(src_points,
r=radius_max/earth_radius,
return_distance=True)
Now you can manipulate the results to get what you want
# create a dataframe build with
# index based on row position of the building in buildings
# column row_stop is the row position of the stop
# dist is the distance
closest_dist = pd.concat([pd.Series(ind_radius).explode().rename('row_stop'),
pd.Series(dist_radius).explode().rename('dist')*earth_radius],
axis=1)
print (closest_dist.head())
# row_stop dist
#0 1131 180.522
#1 NaN NaN
#2 64 174.744
#2 61 119.426
#3 532 106.763
# merge the dataframe created above with the original data stops
# to get names, id, ... note: the index must be reset as in closest_dist
# it is position based
closest_stop = closest_dist.merge(stops.reset_index(drop=True),
left_on='row_stop', right_index=True, how='left')
print (closest_stop.head())
# row_stop dist stop_name stop_lat stop_lon stop_id \
#0 1131 180.522 Muusantori 60.20749 24.85745 1304138.0
#1 NaN NaN NaN NaN NaN NaN
#2 64 174.744 Senaatintori 60.16896 24.94983 1020455.0
#2 61 119.426 Senaatintori 60.16901 24.95046 1020450.0
#3 532 106.763 Veturitie 60.20661 24.92968 1174112.0
#
# geometry
#0 POINT (24.85745 60.20749)
#1 None
#2 POINT (24.94983 60.16896)
#2 POINT (24.95046 60.16901)
#3 POINT (24.92968 60.20661)
Finally join back to buildings
# join buildings with reset_index with
# closest_stop as index in closest_stop are position based
final_df = buildings.reset_index(drop=True).join(closest_stop, rsuffix='_stop')
print (final_df.head(10))
# name geometry row_stop dist stop_name \
# 0 None POINT (24.85584 60.20727) 1131 180.522 Muusantori
# 1 Uimastadion POINT (24.93045 60.18882) NaN NaN NaN
# 2 None POINT (24.95113 60.16994) 64 174.744 Senaatintori
# 2 None POINT (24.95113 60.16994) 61 119.426 Senaatintori
# 3 Hartwall Arena POINT (24.92918 60.20570) 532 106.763 Veturitie
# stop_lat stop_lon stop_id geometry_stop
# 0 60.20749 24.85745 1304138.0 POINT (24.85745 60.20749)
# 1 NaN NaN NaN None
# 2 60.16896 24.94983 1020455.0 POINT (24.94983 60.16896)
# 2 60.16901 24.95046 1020450.0 POINT (24.95046 60.16901)
# 3 60.20661 24.92968 1174112.0 POINT (24.92968 60.20661)
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