# 6. Corridor segmentation

    library(rcrisp)
    library(sf)

    bucharest_osm <- get_osm_example_data()
    bucharest_dem <- get_dem_example_data()

    if (any(is.null(bucharest_osm), is.null(bucharest_dem))) {
      cat("NOTE: Example data was not found; ",
          "subsequent code chunks will be skipped.\n", sep = "")
      knitr::opts_chunk$set(eval = FALSE)
    }

For a more detailed analysis of an urban river corridor, corridor-level delineation may not be sufficient. The corridor needs to be subdivided into smaller morphological units. Segmentation is a process of subdividing the corridor by using major transversal road or rail infrastructure lines.

By default, the all-in-one function `delineate()` only returns the corridor boundary. The corridor can be segmented either by setting the argument `segments = TRUE` in `delineate()` or by using the `delineate_segments()` function in a separate step.

To demonstrate this as a separate step, we will use the `bucharest_dambovita$corridor` from the package data, as well as `bucharest_osm$streets` and `bucharest_osm$railways` from rcrisp example data as input.

We first prepare the network and select all the streets and railways that cover the river corridor plus a small buffer region (see also `vignette("network-preparation")`):

    # Add a buffer region around the corridor
    corridor_buffer <- sf::st_buffer(bucharest_dambovita$corridor, 500)

    # Filter the streets and railwayas to the buffer area
    streets <- bucharest_osm$streets |>
      sf::st_filter(corridor_buffer, .predicate = sf::st_covered_by)
    railways <- bucharest_osm$railways |>
      sf::st_filter(corridor_buffer, .predicate = sf::st_covered_by)

    # Build combined street and railway network
    network_filtered <- rbind(streets, railways) |>
      as_network()

We then delineate segments in the corridor. The algorithm spits the corridor using river-crossing transversal edges that form continuous lines in the network:

    segmented_corridor <-
      delineate_segments(bucharest_dambovita$corridor,
                         network_filtered,
                         st_geometry(bucharest_osm$river_centerline))
    plot(st_geometry(streets))
    plot(segmented_corridor, border = "orange", lwd = 3, add = TRUE)