st_read: read simple features from file or database

Description

read simple features from file or database

read PostGIS table directly through DBI and RPostgreSQL interface, converting binary

Usage

st_read(dsn, layer = default_layer(dsn), ..., options = NULL, quiet = FALSE, iGeomField = 1L, type = 0, promote_to_multi = TRUE)
st_read_db(conn = NULL, table, query = paste("select * from ", table, ";"), geom_column = NULL, EWKB, ...)

Arguments

dsn

data source name (interpretation varies by driver - for some drivers, dsn is a file name, but may also be a folder)

layer

layer name (varies by driver, may be a file name without extension); see details

...

parameter(s) passed on to st_as_sf

options

character; driver dependent dataset open options; multiple options supported.

quiet

logical; suppress info on name, driver, size and spatial reference

iGeomField

integer; in case of multiple geometry fields, which one to take?

type

integer; ISO number of desired simple feature type; see details. If left zero, in case of mixed feature geometry types, conversion to the highest numeric type value found will be attempted.

promote_to_multi

logical; in case of a mix of LineString and MultiLineString, or of Polygon and MultiPolygon, convert all to the Multi variety; defaults to TRUE

conn

open database connection

table

table name

query

SQL query to select records

geom_column

character or integer: indicator of name or position of the geometry column; if not provided, the last column of type character is chosen

EWKB

logical; is the WKB is of type EWKB? defaults to TRUE if conn is of class codePostgreSQLConnection or PqConnection

Value

object of class sf

Details

for iGeomField, see also https://trac.osgeo.org/gdal/wiki/rfc41_multiple_geometry_fields; for type values see https://en.wikipedia.org/wiki/Well-known_text#Well-known_binary, but note that not every target value may lead to succesful conversion. The typical conversion from POLYGON (3) to MULTIPOLYGON (6) should work; the other way around (type=3), secondary rings from MULTIPOLYGONS may be dropped without warnings.

layer name may be guessed in some cases e.g. when dsn contains the full path of a geopackage or a shapefile (with extension .shp), and it will try to do so; this may fail in other cases, though; it is often a good idea to specify both basename and layer name.

in case geom_column is missing: if table is missing, this function will try to read the name of the geometry column from table geometry_columns, in other cases, or when this fails, the geom_column is assumed to be the last column of mode character.

Examples

if (Sys.getenv("USER") %in% c("edzer", "travis")) { # load meuse to postgis
 library(sp)
 example(meuse, ask = FALSE, echo = FALSE)
 st_write(st_as_sf(meuse), "PG:dbname=postgis", "meuse", driver = "PostgreSQL", 
   options = "OVERWRITE=true")
 (s = st_read("PG:dbname=postgis", "meuse"))
 summary(s)
}
# nc = st_read(system.file("gpkg/nc.gpkg", package="sf"), "nc.gpkg", crs = 4267)
nc = st_read(system.file("shape/nc.shp", package="sf"), "nc", crs = 4267)
summary(nc)
if (Sys.getenv("USER") %in% c("travis", "edzer")) {
  library(RPostgreSQL)
  conn = dbConnect(PostgreSQL(), dbname = "postgis")
  st_read_db(conn, query = "select * from meuse limit 3;")
  dbDisconnect(conn)
}