PostGIS setup

geojson_read() allows you to get data out of a PostgreSQL database set up with PostGIS. Below are steps for setting up data that we can at the end query with geojson_read()

Details

If you don't already have PostgreSQL or PostGIS:

• PostgreSQL installation: https://www.postgresql.org/download/

• PostGIS installation: https://postgis.net/install/

Once you have both of those installed, you can proceed below.

Examples

if (FALSE) { # \dontrun{
if (requireNamespace("DBI") && requireNamespace("RPostgres")) {
  library("DBI")
  library("RPostgres")

  # Create connection
  conn <- tryCatch(dbConnect(RPostgres::Postgres()), error = function(e) e)
  if (inherits(conn, "PqConnection")) {

    # Create database
    dbSendQuery(conn, "CREATE DATABASE postgistest")

    # New connection to the created database
    conn <- dbConnect(RPostgres::Postgres(), dbname = "postgistest")

    # Initialize PostGIS in Postgres
    dbSendQuery(conn, "CREATE EXTENSION postgis")
    dbSendQuery(conn, "SELECT postgis_full_version()")

    # Create table
    dbSendQuery(conn, "CREATE TABLE locations(loc_id integer primary key
   , loc_name varchar(70), geog geography(POINT) );")

    # Insert data
    dbSendQuery(conn, "INSERT INTO locations(loc_id, loc_name, geog)
 VALUES (1, 'Waltham, MA', ST_GeogFromText('POINT(42.40047 -71.2577)') )
   , (2, 'Manchester, NH', ST_GeogFromText('POINT(42.99019 -71.46259)') )
   , (3, 'TI Blvd, TX', ST_GeogFromText('POINT(-96.75724 32.90977)') );")


    # Get data (notice warnings of unknown field type for geog)
    dbGetQuery(conn, "SELECT * from locations")


    # Once you're setup, use geojson_read()
    conn <- dbConnect(RPostgres::Postgres(), dbname = "postgistest")
    state <- "SELECT row_to_json(fc)
 FROM (SELECT 'FeatureCollection' As type, array_to_json(array_agg(f)) As features
 FROM (SELECT 'Feature' As type
    , ST_AsGeoJSON(lg.geog)::json As geometry
    , row_to_json((SELECT l FROM (SELECT loc_id, loc_name) As l
      )) As properties
   FROM locations As lg   ) As f )  As fc;"
    json <- geojson_read(conn, query = state, what = "json")

    ## map the geojson with map_leaf()
    map_leaf(json)
  }
}
} # }