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rcoordinatesspatialr-sf

is point with coordinate x,y within osmdata multipolygon in R?

I am trying to assess if a point coordinate x,y is in a multipolygon obtain through api from osmdata library in R.

in dat1 I get the multipolygon from OSM. in ptCoord I enter the point to assess and set the crs.

both variable are sfc objects, however I can't seems to assess if the point is in the multipolygon using sf::st_contains

any help would be greatly appreciated, I spend over 2 hours browsing through the online documentation and ressources unsuccessfully.


dat1 <- opq_osm_id (type = "relation", id = 1237758) %>%
    opq_string () %>%
    osmdata_sf ()

ptCoord <- ptCoord = st_sfc(st_point(c(10.713097, 47.54761)), crs = 4326)


sf::st_contains(dat1$osm_multipolygons, ptCoord)
#Sparse geometry binary predicate list of length 1, where the predicate
#was `contains'
#1: (empty)
Solution

  • the results seems to be right, the point is not in the polygon, see:

    library(osmdata)
#> Data (c) OpenStreetMap contributors, ODbL 1.0. https://www.openstreetmap.org/copyright
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
library(ggplot2)

dat1 <- opq_osm_id(type = "relation", id = 1237758) %>%
  opq_string() %>%
  osmdata_sf()


poly <- st_transform(dat1$osm_multipolygons, 4326)
#> Warning in CPL_transform(x, crs, aoi, pipeline, reverse, desired_accuracy, :
#> GDAL Error 1: PROJ: proj_as_wkt: DatumEnsemble can only be exported to
#> WKT2:2019



ptCoord <- st_sfc(st_point(c(10.713097, 47.54761)), crs = 4326)
sf::st_contains(poly, ptCoord)
#> Sparse geometry binary predicate list of length 1, where the predicate
#> was `contains'
#>  1: (empty)

sf::st_contains(poly, ptCoord, sparse = FALSE)
#>      [,1]
#> [1,] FALSE

ggplot(poly) +
  geom_sf() +
  geom_sf(data = ptCoord)

    The plot shows that ptCoord is not in poly, so the results is empty. See how this would behave if we select a point that is in the polygon (I sample this with st_sample())

      
# Check alt
set.seed(1234)
alt <- st_sample(poly, size=1)

ggplot(poly) +
  geom_sf() +
  geom_sf(data = alt)


    
# This one is contained

sf::st_contains(poly, alt)
#> Sparse geometry binary predicate list of length 1, where the predicate
#> was `contains'
#>  1: 1


sf::st_contains(poly, alt, sparse = FALSE)
#>      [,1]
#> [1,] TRUE

    So in this case the result is that alt is contained in the polygon 1 ot the object poly

    Created on 2023-04-18 with reprex v2.0.2