Multiple geometries returned for trips along same road

[grobins]

I have a local server running osrm, and I'm trying to pass in 1000 trips with a start & end location, and 100 waypoints.

I want to return the trips with their geometries snapped to the road, so that I can join by location in QGIS and produce a heatmap of the number of trips on each road.

When I run the following code I get back the trips as pictured

trip_ids <- unique(trip_points$trip_id)

for (i in 1:length(trip_ids)) {

  testtrip    <- trip_points %>% filter(trip_id == trip_ids[i])
  fl          <- testtrip %>% rowid_to_column() %>% slice(c(1,n()))
  mid         <- testtrip %>% rowid_to_column() %>% slice_sample(n=100)
  testtrip    <- bind_rows(fl, mid) %>% arrange(rowid)
  
  testtrip.sf <- st_as_sf(testtrip, coords = c("longitude", "latitude"), crs = 4326)
  route2      <- osrmRoute(loc = testtrip.sf, returnclass = "sf", overview = 'full')

  if (i == 1) {
    results <- route2
  } else {
    results <- bind_rows(results, route2)
  }
}

results %>%
  mutate(linestring = st_as_text(st_sfc(results$geometry), crs = 4326)) %>%
  as.data.frame() %>%
  select(-geometry) %>%
  write_delim("test_snapped_linestrings_local.csv", ";")

I expected the same geometry to be returned for each trip in the image, but as you can see many are offset. Any help would be appreciated

[rCarto]

I would have said that osrmRoute(..., overview = "full") was the solution, but you use it already.
Otherwise, maybe this part could be problematic, specifically the mutate part :

results %>%
  mutate(linestring = st_as_text(st_sfc(results$geometry), crs = 4326)) %>%
  as.data.frame() %>%
  select(-geometry) %>%
  write_delim("test_snapped_linestrings_local.csv", ";")

Can you post a reproducible example please.

[grobins]

Thanks, that helped a lot...

I changed from writing out a WKT to using results %>% st_write('test_snapped_linestrings_local.shp') and it's now perfect.

the highlighted line actually has 197 overlapping

I also changed from osrmRoute() to osrmTrip() - not too sure what the difference is rn but this seems to work ok

[rCarto]

Nice!
osrmRoute() computes the shortest path between 2 (or more) ordered points.
osrmTrip() computes the shortest trip between a set of unordered points (the traveling salesperson problem).
So I think you were right to use osrmRoute() first.