R sparql demo for geoconnex

r-geoconnex.R

##packages used
require(sf)
require(SPARQL)
# remotes::install_github("cran/SPARQL") this is archived by cran grrrr
require(mapview)
require(dplyr)
library(stringi)

# start gage
gage_uri <- "https://geoconnex.us/ref/gages/1118104"

start_gage <- sf::read_sf(gage_uri)
#define function that takes a gage uri and feeds it into a SPARQL query that 
#identifies all features that have the same linearElement as a referencedPosition
#and returns those features and the mainstem as sf objects

find_mainstem_from_gage <- function(gage_uri){
  endpoint <- "https://graph.geoconnex.us/repositories/iow"
  query <- paste0("PREFIX hyf: <https://www.opengis.net/def/schema/hy_features/hyf/> 
                  PREFIX schema: <https://schema.org/> 
                  PREFIX geo: <http://www.opengis.net/ont/geosparql#>  
                  select DISTINCT ?mainstem ?gage ?name (str(?gwkt) AS ?gage_geom) (str(?mswkt) AS ?mainstem_geom) 
                  where {    <",
                  gage_uri,
                  "> hyf:referencedPosition ?rp .
                  ?rp hyf:HY_IndirectPosition ?ip .     
                  ?ip hyf:linearElement ?mainstem .     
                  BIND (?mainstem as ?target)     
                  ?gage hyf:referencedPosition ?rp2 .    
                  ?rp2 hyf:HY_IndirectPosition ?ip2.     
                  ?ip2 hyf:linearElement ?target .    
                  ?mainstem schema:name ?name .     
                  ?mainstem geo:hasGeometry ?msgeom .     
                  ?msgeom geo:asWKT ?mswkt .    
                  ?gage geo:hasGeometry ?ggeom .     
                  ?ggeom geo:asWKT ?gwkt         }")
  df <- SPARQL::SPARQL(endpoint,query)$results
  sf_gage <- sf::st_as_sf(df,wkt="gage_geom",crs=4326)
  sf_gage <- dplyr::select(sf_gage,-mainstem_geom)
  sf_mainstem <- sf::st_as_sf(df[1,],wkt="mainstem_geom",crs=4326)
  list <- list(sf_gage,sf_mainstem)
  return(list)
}

hyperlink <- function(url){
  link <- paste0("<a href=",
                 gsub("<","",gsub(">","",url)),
                 ">",
                 gsub("<","",gsub(">","",url)),
                 "</a>")
}
#call function
iowa <- find_mainstem_from_gage(gage_uri)
iowa[[1]]$gage <- hyperlink(iowa[[1]]$gage)
iowa[[1]]$mainstem <- NULL
iowa[[2]]$mainstem <- hyperlink(iowa[[2]]$mainstem)
iowa[[2]]$gage <- NULL

#map
mapview(iowa[1], layer.name="gages") + mapview(iowa[2],layer.name="mainstem") + mapview(start_gage,layer.name="Start Gage",col.regions="red")