readOGR: Read OGR vector maps into Spatial objects

Description

The function reads an OGR data source and layer into a suitable Spatial vector object. It can only handle layers with conformable geometry features (not mixtures of points, lines, or polygons in a single layer). It will set the spatial reference system if the layer has such metadata.

If reading a shapefile, the data source name (dsn= argument) is the folder (directory) where the shapefile is, and the layer is the name of the shapefile (without the .shp extension). For example to read bounds.shp from C:/Maps, do map <- readOGR(dsn="C:/Maps", layer="bounds"). The logic behind this is that typically one keeps all the shapefiles for a project in one folder (directory).

As noted below, for other file type drivers, the dsn= argument is interpreted differently, and may be the file name itself, as for example with the GPX driver for reading GPS data as layer="tracks" lines or layer="track_points" points.

Usage

readOGR(dsn, layer, verbose = TRUE, p4s=NULL, 
 stringsAsFactors=as.logical(NA), 
 drop_unsupported_fields=FALSE,
 pointDropZ=FALSE, dropNULLGeometries=TRUE,
 useC=TRUE, disambiguateFIDs=FALSE, addCommentsToPolygons=TRUE,
 encoding=NULL, use_iconv=FALSE, swapAxisOrder=FALSE, require_geomType = NULL,
 integer64="no.loss", GDAL1_integer64_policy=FALSE, morphFromESRI = NULL,
 dumpSRS = FALSE, enforce_xy = NULL, D3_if_2D3D_points=FALSE, missing_3D=0)
ogrInfo(dsn, layer, encoding=NULL,
 use_iconv=FALSE, swapAxisOrder=FALSE, require_geomType = NULL,
 morphFromESRI = NULL, dumpSRS = FALSE, enforce_xy = NULL,
 D3_if_2D3D_points=FALSE)
ogrFIDs(dsn, layer)
ogrDrivers()
OGRSpatialRef(dsn, layer, morphFromESRI=NULL, dumpSRS = FALSE, driver = NULL,
 enforce_xy = NULL, get_source_if_boundcrs=TRUE)
ogrListLayers(dsn)
# S3 method for ogrinfo
print(x, ...)

Value

A Spatial object is returned suiting the vector data source, either a SpatialPointsDataFrame (using an AttributeList for its data slot directly), a SpatialLinesDataFrame, or a SpatialPolygonsDataFrame.

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). From rgdal 1.2.*, layer may be missing, in which case ogrListLayers examines the dsn, and fails if there are no layers, silently reads the only layer if only one layer is found, and reads the first layer if multiple layers are present, issuing a warning that layer should be given explicitly.
verbose: report progress
p4s: PROJ4 string defining CRS, if default NULL, the value is read from the OGR data set
stringsAsFactors: logical: should character vectors be converted to factors? Default NA, which uses the deprecated default.stringsAsFactors() in R < 4.1.0 (see link[base]{data.frame}). Before R 4, strings were converted to factors by default, as argument value TRUE. See https://developer.r-project.org/Blog/public/2020/02/16/stringsasfactors/index.html for details of changes.
drop_unsupported_fields: default FALSE, if TRUE skip fields other than String, Integer, and Real; Date, Time and DateTime are converted to String
pointDropZ: default FALSE, if TRUE, discard third coordinates for point geometries; third coordinates are alway discarded for line and polygon geometries
dropNULLGeometries: default TRUE, drop both declared NULL geometries, and empty geometries with no coordinates; if FALSE, return a data frame with the attribute values of the NULL and empty geometries. From 1.3-6, setting FALSE also works when there are no geometries at all, returning a data.frame including all FIDs
useC: default TRUE, if FALSE use original interpreted code in a loop
disambiguateFIDs: default FALSE, if TRUE, and FID values are not unique, they will be set to unique values 1:N for N features; problem observed in GML files
addCommentsToPolygons: default TRUE, may be set FALSE for legacy behaviour; used to indicate which interior rings are holes in which exterior rings in conformance with OGC SFS specifications
encoding: default NULL, if set to a character string, and the driver is “ESRI Shapefile”, and use_iconv is FALSE, it is passed to the CPL Option “SHAPE_ENCODING” immediately before reading the DBF of a shapefile. If use_iconv is TRUE, and encoding is not NULL, it will be used to convert input strings from the given value to the native encoding for the system/platform.
use_iconv: default FALSE; if TRUE and encoding is not NULL, it will be used to convert input strings from the given value to the native encoding for the system/platform.
swapAxisOrder: default FALSE, if TRUE, treat y coordinate as Easting, x as Northing, that is the opposite to the assumed order; this may be needed if some OGR read drivers do not behave as expected
require_geomType: , default NULL, if one of: c("wkbPoint", "wkbLineString", "wkbPolygon"), then in input with multiple geometry types, the chosen type will be read
integer64: default “no.loss” (from rgdal 1.2.*). From GDAL 2, fields to be read may also take Integer64 values. As R has no such storage mode, three options are offered, analogous with type.convert for numeric conversion: “allow.loss” which clamps to 32-bit signed integer (default < rgdal 1.2), “warn.loss” - as “allow.loss” but warns when clamping occurs, and “no.loss”, which reads as a character string using the formatting applied by default by GDAL (default >= rgdal 1.2). The use of 64-bit integers is usually a misunderstanding, as such data is almost always a long key ID.
GDAL1_integer64_policy: default FALSE, if TRUE, Integer64 fields are read as doubles
morphFromESRI: default NULL, morph from ESRI WKT1 dialect
dumpSRS: dump SRS to stdout from inside GDAL to debug conversion - developer use only
enforce_xy: (PROJ6+/GDAL3+) either use global setting (default NULL) or override policy for coordinate ordering easting/x as first axis, northing/y as second axis.
get_source_if_boundcrs: The presence of the +towgs84= key in a Proj4 string projargs= argument value may promote the output WKT2 CRS to BOUNDCRS for PROJ >= 6 and GDAL >= 3, which is a coordinate operation from the input datum to WGS84. This is often unfortunate, so a PROJ function is called through rgdal to retrieve the underlying source definition.
D3_if_2D3D_points: https://github.com/r-spatial/sf/issues/1683 case of mixed 2D/3D track points - set TRUE to 3D to pass
missing_3D: default 0, may be finite real numbers; https://github.com/r-spatial/sf/issues/1683
driver: default NULL, driver found using ogrListLayers from the data source; otherwise already known and passed through from a calling function
x: ogrinfo object
...: other arguments to print method

Author

Roger Bivand

Details

The drivers available will depend on the installation of GDAL/OGR, and can vary; the ogrDrivers() function shows which are available, and which may be written (but all are assumed to be readable). Note that stray files in data source directories (such as *.dbf) may lead to suprious errors that accompanying *.shp are missing.

References

https://gdal.org/drivers/vector/index.html, https://resources.oreilly.com/examples/9780596008659

Examples

Run this code

set_thin_PROJ6_warnings(TRUE)
ogrDrivers()
dsn <- system.file("vectors", package = "rgdal")[1]
ogrListLayers(dsn)
ogrInfo(dsn)
ogrInfo(dsn=dsn, layer="cities")
owd <- getwd()
setwd(dsn)
ogrInfo(dsn="cities.shp")
ogrInfo(dsn="cities.shp", layer="cities")
setwd(owd)
ow <- options("warn")$warn
options("warn"=1)
cities <- readOGR(dsn=dsn, layer="cities")
str(slot(cities, "data"))
if (new_proj_and_gdal()) comment(slot(cities, "proj4string"))
cities$POPULATION <- type.convert(as.character(cities$POPULATION),
  na.strings="-99", numerals="no.loss")
str(slot(cities, "data"))
cities <- readOGR(dsn=dsn, layer="cities", GDAL1_integer64_policy=TRUE)
str(slot(cities, "data"))
options("warn"=ow)
summary(cities)
table(Encoding(as.character(cities$NAME)))
ogrInfo(dsn=dsn, layer="kiritimati_primary_roads")
OGRSpatialRef(dsn=dsn, layer="kiritimati_primary_roads")
kiritimati_primary_roads <- readOGR(dsn=dsn, layer="kiritimati_primary_roads")
summary(kiritimati_primary_roads)
if (new_proj_and_gdal()) comment(slot(kiritimati_primary_roads, "proj4string"))
ogrInfo(dsn=dsn, layer="scot_BNG")
OGRSpatialRef(dsn=dsn, layer="scot_BNG")
scot_BNG <- readOGR(dsn=dsn, layer="scot_BNG")
summary(scot_BNG)
if (new_proj_and_gdal()) comment(slot(scot_BNG, "proj4string"))
if ("GML" %in% ogrDrivers()$name) {
  dsn <- system.file("vectors/airports.gml", package = "rgdal")[1]
  airports <- try(readOGR(dsn=dsn, layer="airports"))
  if (!inherits(airports, "try-error")) {
    summary(airports)
    if (new_proj_and_gdal()) comment(slot(airports, "proj4string"))
  }
}
dsn <- system.file("vectors/ps_cant_31.MIF", package = "rgdal")[1]
ogrInfo(dsn=dsn, layer="ps_cant_31")
ps_cant_31 <- readOGR(dsn=dsn, layer="ps_cant_31")
summary(ps_cant_31)
sapply(as(ps_cant_31, "data.frame"), class)
if (new_proj_and_gdal()) comment(slot(ps_cant_31, "proj4string"))
ps_cant_31 <- readOGR(dsn=dsn, layer="ps_cant_31", stringsAsFactors=FALSE)
summary(ps_cant_31)
sapply(as(ps_cant_31, "data.frame"), class)
dsn <- system.file("vectors/Up.tab", package = "rgdal")[1]
ogrInfo(dsn=dsn, layer="Up")
Up <- readOGR(dsn=dsn, layer="Up")
summary(Up)
if (new_proj_and_gdal()) comment(slot(Up, "proj4string"))
dsn <- system.file("vectors/test_trk2.gpx", package = "rgdal")[1]
test_trk2 <- try(readOGR(dsn=dsn, layer="tracks"))
if (!inherits(test_trk2, "try-error")) {
  summary(test_trk2)
  if (new_proj_and_gdal()) comment(slot(test_trk2, "proj4string"))
}
test_trk2pts <- try(readOGR(dsn=dsn, layer="track_points"))
if (!inherits(test_trk2pts, "try-error")) {
  summary(test_trk2pts)
  if (new_proj_and_gdal()) comment(slot(test_trk2pts, "proj4string"))
}
dsn <- system.file("vectors", package = "rgdal")[1]
ogrInfo(dsn=dsn, layer="trin_inca_pl03")
birds <- readOGR(dsn=dsn, layer="trin_inca_pl03")
summary(birds)
if (new_proj_and_gdal()) comment(slot(birds, "proj4string"))
dsn <- system.file("vectors/PacoursIKA2.TAB", package = "rgdal")[1]
try(ogrInfo(dsn, "PacoursIKA2"))
ogrInfo(dsn, "PacoursIKA2", require_geomType="wkbPoint")
plot(readOGR(dsn, "PacoursIKA2", require_geomType="wkbLineString"), col="red")
plot(readOGR(dsn, "PacoursIKA2", require_geomType="wkbPoint"), add=TRUE)
odir <- getwd()
setwd(system.file("vectors", package = "rgdal")[1])
ow <- options("warn")$warn
options("warn"=1)
ogrInfo("test64.vrt", "test64")
str(readOGR("test64.vrt", "test64", verbose=FALSE, integer64="allow.loss")$val)
str(readOGR("test64.vrt", "test64", verbose=FALSE, integer64="warn.loss")$val)
str(readOGR("test64.vrt", "test64", verbose=FALSE, integer64="no.loss")$val)
str(readOGR("test64.vrt", "test64", verbose=FALSE, stringsAsFactors=FALSE,
 integer64="no.loss")$val)
setwd(odir)
options("warn"=ow)

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