agila5/example_sfnetworks.md

## example_sfnetworks.md

      
    Raw
  

              example_sfnetworks.md
            
          
    # packages
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1
library(sfnetworks)
library(tidygraph)
#> 
#> Attaching package: 'tidygraph'
#> The following object is masked from 'package:stats':
#> 
#>     filter

# data
download.file("https://github.com/JovaniSouza/JovaniSouza5/raw/master/Test.zip", "Test.zip")
download.file("https://github.com/ropensci/stplanr/releases/download/0.6.1/Example.zip", "Example.zip")
unzip("Example.zip")
unzip("Test.zip")

roads = st_read("Test/regionbrazil.shp", quiet = TRUE)
points = st_read("Example/Points/Points.shp", quiet = TRUE)
roads_trf = st_transform(roads, st_crs(points)) %>% 
  st_cast("LINESTRING")
#> Warning in st_cast.sf(., "LINESTRING"): repeating attributes for all sub-
#> geometries for which they may not be constant

# build sfnetwork
net = as_sfnetwork(roads_trf, directed = FALSE) %>%
  activate("edges") %>%
  dplyr::mutate(weight = edge_length())

# Estimate shortest path between 3rd point and 4th point
st_shortest_paths(net, points[3, ], points[4, ])
#> although coordinates are longitude/latitude, st_nearest_feature assumes that they are planar
#> although coordinates are longitude/latitude, st_nearest_feature assumes that they are planar
#> $vpath
#> $vpath[[1]]
#> + 1/98316 vertex, from 1f5f38c:
#> [1] 65808
#> 
#> 
#> $epath
#> NULL
#> 
#> $predecessors
#> NULL
#> 
#> $inbound_edges
#> NULL

# It looks like there is not path, but why? The problem is that both points are
# associated to the same node:
st_nearest_feature(points[3, ], net %>% activate(nodes) %>% st_as_sf())
#> although coordinates are longitude/latitude, st_nearest_feature assumes that they are planar
#> [1] 65808
st_nearest_feature(points[4, ], net %>% activate(nodes) %>% st_as_sf())
#> although coordinates are longitude/latitude, st_nearest_feature assumes that they are planar
#> [1] 65808

# So it's not a problem of the function of the package but simply both points
# are matched with the same node so there is no "shortest path".
^{Created on 2020-07-12 by the reprex package (v0.3.0)}