generate lat-lon along a line shapefile

I have a road shapefile from the following location

https://www.globio.info/download-grip-dataset

I downloaded the shapefile for North America and subset the roads for Canada as follows:

  library(raster)
  library(ggplot2)
  library(sf)
  library(sp)
  road <- read_sf(file.path(dir_ls$base,"roadshapefile","GRIP4_Region1_vector_shp","GRIP4_region1.shp"))

  road_canada <- road %>%
                  dplyr::filter(GP_RTP %in% c(1,2), # 1 for highways 
                                GP_REX == 1, # 1 for Open 
                                GP_RRG == 1, # 1 is for Canada
                                GP_RCY == 124 # for Canada
                  ) 

  ggplot(road_canada) + geom_sf()

I want to generate 20 random latlon along the roads

  spsample(road_canada, n=20, type="random")

  Error in (function (classes, fdef, mtable)  : 
              unable to find an inherited method for function ‘spsample’ for signature ‘"sf"’

I understand the error that beacause of sf class, this method is not working. I am not aware of any other method that will enable me to do it and wondered if anyone knows any alternative?

Solution

Using st_sample works, but wasn't totally straightforward. The size of the road data makes it hard to work with in-memory.

Below the road_canada object is simplified, uses only the geometry column, combined, sampled, and finally had to be cast to POINT to get the coordinates to show up.

# Use only the geometry column, simplify for a smaller object.
road_canada <- st_geometry(road_canada) %>% rmapshaper::ms_simplify()

road_sample <- road_canada %>%
  st_combine() %>%
  st_sample(20) %>%  ## Returns MULTIPOINT EMPTY, fixed with st_cast('POINT')
  st_cast('POINT')

head(road_sample)
#Geometry set for 6 features 
#Geometry type: POINT
#Dimension:     XY
#Bounding box:  xmin: -117.3209 ymin: 52.32145 xmax: -109.5217 ymax: 58.59094
#Geodetic CRS:  WGS 84
#First 5 geometries:
#POINT (-109.5217 52.4055)
#POINT (-117.3209 52.32145)
#POINT (-112.3959 53.01749)
#POINT (-112.9708 53.5703)
#POINT (-113.9 54.38767)