r语言 - 地理编码:找到两组位置之间距离的有效方法

Question

我有一组不同个人的位置坐标，以及另一组不同选票投递箱的坐标。我在查他们住处和最近的dropbox之间的距离。我附上了一份我现在必须处理的代码副本——它是从另一个堆栈溢出示例复制的。然而，它不是很有效，因为我正在使用的数据集有数百万行，代码依赖于找到所有可能的坐标组合，然后拉出最小的距离。有没有更有效的方法来处理这个问题?

我现在拥有的:

# Made-Up Data
library(geosphere)
library(tidyverse)
geo_voters <- data.frame(voter_id = c(12345, 45678, 89011)
long=c(-43.17536, -43.17411, -43.36605),
lat=c(-22.95414, -22.9302, -23.00133))
geo_dropoff_boxes <- data.frame(long=c(-43.19155, -43.33636, -67.45666),
lat=c(-22.90353, -22.87253, -26,78901))

# Code to find the distance between voters, and the dropoff boxes
# Order into a newdf as needed first.
# First, the voters:  
voter_addresses <- data.frame(voter_id = as.character(geo_voters$voter_id),
lon_address = geo_voters$long,
lat_address = geo_voters$lat
)
# Second, the polling locations: 
polling_address <- data.frame(place_number = 1:nrow(geo_dropoff_boxes),
lon_place = geo_dropoff_boxes$long,
lat_place = geo_dropoff_boxes$lat
)
# Create nested dfs: 
voter_nest <- nest(voter_addresses, -voter_id, .key = 'voter_coords')
polling_nest <- nest(polling_address, -place_number, .key = 'polling_coords')
# Combine for combinations: 
data_master <- crossing(voter_nest, polling_nest)
# Calculate shortest distance: 
shortest_dist <- data_master %>% 
mutate(dist = map2_dbl(voter_coords, polling_coords, distm)) %>% 
group_by(voter_id) %>% 
filter(dist == min(dist)) %>%
mutate(dist_km = dist/1000,
voter_id = as.character(voter_id)) %>%
select(voter_id, dist_km)

Answer 1

sf包使这很简单。st_as_sf()函数将latlong值的数据帧转换为地理参考点，st_distance()函数计算它们之间的距离。在运行st_as_sf()时，需要指定一个坐标参考系统。看起来您正在使用纬度和经度，所以我指定crs="epsg:4326"，这是最常用的纬度/经度引用。

library( sf )
geo_voters <- data.frame(voter_id = c(12345, 45678, 89011)
long=c(-43.17536, -43.17411, -43.36605),
lat=c(-22.95414, -22.9302, -23.00133))
geo_dropoff_boxes <- data.frame(long=c(-43.19155, -43.33636, -67.45666),
lat=c(-22.90353, -22.87253, -26.78901))
# convert the data to sf features
geo_voters = st_as_sf( geo_voters, coords=c('long', 'lat'), crs="epsg:4326" )
geo_dropoff_boxes = st_as_sf( geo_dropoff_boxes, coords=c('long', 'lat'), crs="epsg:4326" )
# calculate the distances between voters and drop boxes
dist = st_distance( geo_voters, geo_dropoff_boxes )
print(dist)

现在每一行代表一个选民，每一列代表他们到投注箱的距离(单位为米):

Units: [m]
[,1]     [,2]    [,3]
[1,]  5866.745 18821.87 2482400
[2,]  3461.945 17813.57 2483210
[3,] 20916.618 14641.09 2462186