Nearest locations to multiple routes - r

Question

I'd like to get the nearest location from each of a list of routes and the distance from the route to the place. I think I can do this via SF but am not sure how. In the sample data there are 19 separate routes.
install.packages("sf")
install.packages("sfheaders")
library(sf)
routeData <- read.csv("https://www.dropbox.com/s/vtj8wvcqxj52pbl/SpainActivityRoutes.csv?dl=1")
# Convert routes to SF
sfheaders::sf_multipolygon(
obj = spainActivityRoutes
, multipolygon_id = "id"
, x = "lon"
, y = "lat"
)
# Read in locations
locations <- data.frame(id = c(1,2,3),
place = c('Alcudia', 'Puerto de Pollensa', 'Alaro'),
latitude = c(39.85327712, 39.9024565, 39.704459175469395),
longitude = c(3.123974802, 3.080426926, 2.7919874776545694))

Answer 1

Starting with the data:
routeData <- read.csv("https://www.dropbox.com/s/vtj8wvcqxj52pbl/SpainActivityRoutes.csv?dl=1")
split on id, apply a function to create linestring objects, join the list of linestrings using st_sfc to make a spatial vector. Assume these are "GPS" coordinates with EPSG code 4326:
routes = do.call(st_sfc, lapply(split(routeData, routeData$id) , function(d){st_linestring(cbind(d$lon, d$lat))}))
st_crs(routes)=4326
Convert points data frame to spatial points data frame with same coordinate system:
pts = st_as_sf(locations, coords=c("longitude","latitude"), crs=4326)
Now we can get the nearest route to each point:
> nearf = st_nearest_feature(pts, routes)
> nearf
[1] 1 15 19
So the first point is nearest to route 1, the second point route 15, the third point route 19. Now the distances we get by computing the distance from each point in turn to each of those route lines in turn by using st_distance with by_element=TRUE (otherwise it computes the distances from all points to all three routes as a matrix):
> st_distance(pts, routes[st_nearest_feature(pts, routes)], by_element=TRUE)
Units: [m]
[1] 7.888465 27.046029 44.175458
If you want the point on the route nearest to the point data then use st_nearest_points with pairwise=TRUE:
> st_nearest_points(pts, routes[st_nearest_feature(pts, routes)], pairwise=TRUE)
Geometry set for 3 features
Geometry type: LINESTRING
Dimension: XY
Bounding box: xmin: 2.791987 ymin: 39.70412 xmax: 3.124058 ymax: 39.90256
Geodetic CRS: WGS 84
LINESTRING (3.123975 39.85328, 3.124058 39.85331)
LINESTRING (3.080427 39.90246, 3.080143 39.90256)
LINESTRING (2.791987 39.70446, 2.792247 39.70412)
which returns 2-point lines from the test point to the line. You can use functions like st_cast(...,"POINT") to split those into points and get the locations as points.