Distance between all the points to the first point

问题

I have points on a street, and Im trying to calculate the distance between all the points and the first point in the street

Here is my sf object:

library(rgeos)
library(rgdal)
library(sf)
 #I actually have multiple points on a segment of 5 Km
df <- data.frame(lon = c(-121.95, -121.96, -121.97, -121.98), lat = c(37.35,37.36,37.37,37.38)) 
coordinates(df) <- c("lon", "lat")
proj4string(df) <- CRS("+init=epsg:4326") 
df_sf <- st_as_sf(df) %>% st_transform(3488)

I tried st_distance but the distance is not correct. What I sould get is to have each point distance to the begining of the street until the end. So basically it has to go from 0 to the 5000m.

回答1:

If you add the by_element argument to st_distance(), I think you'll get the result you're looking for. If you leave by_element as FALSE (the default), you'll get a matrix instead.

st_distance(x = df_sf, 
            y = df_sf[1,], 
            by_element = TRUE)

Units: [m]
[1]    0.000 1420.606 2841.141 4261.604

Note that the distances differ slightly from the other answer b/c df_sf is projected. If we use the unprojected df object, the distances match:

st_distance(x = df, 
            y = df[1,], 
            by_element = T)

Units: [m]
[1]    0.000 1420.098 2840.125 4260.079

Edit in response to comment re: order

The distances will be in the order of your dataframe. They happen to be in ascending order in your example.

You could add the distances as a new column and then sort on that column using dplyr. Note that the by_element argument is necessary here, as the new column won't accept a matrix as a value.

library(dplyr)
df_sf %>% 
  mutate(dist_to_first = st_distance(x = df_sf, 
                                     y = df_sf[1,], 
                                     by_element = TRUE)) %>% 
  arrange(dist_to_first)

Simple feature collection with 4 features and 1 field
geometry type:  POINT
dimension:      XY
bbox:           xmin: -175068.7 ymin: -72303.08 xmax: -172485.1 ymax: -68913.94
epsg (SRID):    3488
proj4string:    +proj=aea +lat_1=34 +lat_2=40.5 +lat_0=0 +lon_0=-120 +x_0=0 +y_0=-4000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
  dist_to_first                    geometry
1     0.000 [m] POINT (-172485.1 -72303.08)
2  1420.606 [m] POINT (-173346.5 -71173.46)
3  2841.141 [m] POINT (-174207.7 -70043.74)
4  4261.604 [m] POINT (-175068.7 -68913.94)

回答2:

The geosphere package has the distGeo function for this type of calculation:

library(geosphere)

df <- data.frame(lon = c(-121.95, -121.96, -121.97, -121.98), lat = c(37.35,37.36,37.37,37.38)) 

#calculate dist from first row
# to all rows in df
distGeo(df[1,], df)
[1]    0.000 1420.098 2840.125 4260.079

For distGeo, the first column is longitude and the second column is latitude, with the output in meters.

来源：https://stackoverflow.com/questions/59250592/distance-between-all-the-points-to-the-first-point

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