Update riverspace delineation vignette

vignettes/riverspace-delineation.Rmd

@@ -16,4 +16,57 @@ knitr::opts_chunk$set(
 
 ```{r setup}
 library(CRiSp)
+library(osmdata)
+library(sf)
 ```
+
+River space delineation is a delineation step that uses the river and buildings as input to generate a polygon representing the space between the river and the first line of buildings. We will use Bucharest as the study area and the River Dâmbovița as the river.
+
+```{r}
+city_name <- "Bucharest, Romania"   # Be specific and spell as in OSM
+river_name <- "Dâmbovița"           # Spell as it appears in OSM
+epsg_code <- 32635                  # UTM zone 35N
+bbox_buffer <- 2000                 # Buffer around the city boundary in meters
+```
+
+```{r aoi}
+# Get the bounding box from the Nominatim API provided by OSM.
+bb <- getbb(city_name)
+aoi <- define_aoi(bb, epsg_code, bbox_buffer)
+```
+
+```{r city}
+city_boundary <- osmdata_as_sf("place", "city", bb)$osm_multipolygons |>
+  st_transform(epsg_code) |>
+  st_geometry()
+```
+
+```{r river}
+river_centerline <- osmdata_as_sf("waterway", "river", bb)$osm_multilines |>
+  filter(name == river_name) |>
+  st_transform(epsg_code) |>
+  st_geometry() |>
+  st_intersection(st_buffer(aoi, bbox_buffer))
+
+river_surface <- osmdata_as_sf("natural", "water", bb)
+river_surface <- river_surface$osm_multipolygons |>
+  bind_rows(river_surface$osm_polygons) |>
+  st_transform(epsg_code) |>
+  st_filter(river_centerline, .predicate = st_intersects) |>
+  st_geometry() |>
+  st_union()
+```
+
+```{r}
+buildings <- osmdata_as_sf("building", "yes", bb)$osm_multipolygons |>
+  st_transform(epsg_code) |>
+  st_geometry()
+```
+
+The `delineate_riverspace()` function takes the city boundary, river surface and building polygons as input. If no river is found, it will return an error message. If buildings are not found, it will return an unobstructed buffer of a given radius with a warning message. By default, the river space will be capped by the city boundaries. The function returns an sf polygon.
+
+```{r}
+riverspace <- delineate_riverspace(city_boundary, river_surface, buildings)
+```
+
+