R 的坐标对 (UTM) 之间的距离，单位为公里

Question

I have a dataframe with 2 pairs of UTM (32N) coordinates and I need to compute the differences in km between each of them, from origin to destination. I'm trying with sf library, using "by_element" but I obtain an error message "Error in st_distance(data, by_element = TRUE): .missing_y non è TRUE"? What's wrong, If I use it without the "by_element" option, it works and the distance matrix between all coordinates is created. but this is not what I need.

library(sf)
df <- data.frame(id = c(1,2,3), x_origin = c(642683.2, 373775,383881 ), y_origin = c(5082920, 4997274,4994504), x_dest =c(642683.3, 1126050,942763.9 ), y_dest=c(5082920, 4374481,4534235  )) 

data <- st_as_sf(df, coords = c("x_origin", "y_origin"), crs="4326" )

distances <- st_distance(data, by_element = TRUE  )

Answer 1

You have provided x (origin) to st_distance() but no y (destination). And that CRS can't be right, sf doesn't recognise EPSG code if it's a string and 4326 would suggest coordinates are in WGS84 lat/long. Assuming 32632, WGS 84 / UTM zone 32N.

library(sf)
df <- data.frame(id = c(1,2,3), x_origin = c(642683.2, 373775,383881 ), y_origin = c(5082920, 4997274,4994504), x_dest =c(642683.3, 1126050,942763.9 ), y_dest=c(5082920, 4374481,4534235  )) 
origin <- st_as_sf(df, coords = c("x_origin", "y_origin"), crs=32632 )
dest <- st_as_sf(df, coords = c("x_dest", "y_dest"), crs=32632 )

(distances <- st_distance(origin, dest,  by_element = TRUE ))
#> Units: [m]
#>        1        2        3 
#>      0.1 976621.1 724015.0

^{Created on 2023-01-25 with reprex v2.0.2}

Answer 2

First, sf can't know that you are calculating distances between origin and destination by the way you have input the data. Second, the EPSG code for UTM Zone 32N is not 4326 . Third, you should have used crs = st_crs(4326) instead of crs = "4326" .

Use the following piece of code to create the objects needed to calculate the distances you are interested in

library(sf)
df <- data.frame(id = c(1, 2, 3),
                 x_origin = c(642683.2, 373775, 383881),
                 y_origin = c(5082920, 4997274, 4994504),
                 x_dest = c(642683.3, 1126050, 942763.9),
                 y_dest = c(5082920, 4374481, 4534235))

origin <- st_as_sf(df, coords = c("x_origin", "y_origin"),
                   crs = st_crs(32632))
dest <- st_as_sf(df, coords = c("x_dest", "y_dest"),
                 crs = st_crs(32632))

Note the different EPSG code for the CRS.

Next, we calculate the distances (the default of this projection is in meters)

distances <- st_distance(origin, dest, by_element = TRUE)

If you use by_element = FALSE , you get all the pairwise distances.

Lastly, we can use the package units to convert the distances to km (or we can simply divide them by 1000).

units::set_units(distances, "km")
> Units: [km]
> [1]   0.0001 976.6211 724.0150