Convert spatial reference definitions to OGC WKT or PROJJSON

These functions convert various spatial reference formats to Well Known Text (WKT) or PROJJSON.

Usage

epsg_to_wkt(epsg, pretty = FALSE)

srs_to_wkt(srs, pretty = FALSE, gcs_only = FALSE)

srs_to_projjson(
  srs,
  multiline = TRUE,
  indent_width = 2L,
  schema = NA_character_
)

Arguments

epsg: Integer EPSG code.
pretty: Logical value. TRUE to return a nicely formatted WKT string for display to a person. FALSE for a regular WKT string (the default).
srs: Character string containing an SRS definition in various formats (see Details).
gcs_only: Logical value. TRUE to return only the definition of the GEOGCS node of the input srs. Defaults to FALSE (see Note).
multiline: Logical value. TRUE for PROJJSON multiline output (the default).
indent_width: Integer value. Defaults to 2. Only used if multiline = TRUE for PROJJSON output.
schema: Character string containing URL to PROJJSON schema. Can be set to empty string to disable it.

Value

Character string containing OGC WKT.

Details

epsg_to_wkt() exports the spatial reference for an EPSG code to WKT format. Wrapper for OSRImportFromEPSG() in the GDAL Spatial Reference System API with output to WKT.

srs_to_wkt() converts a spatial reference system (SRS) definition in various text formats to WKT. The function will examine the input SRS, try to deduce the format, and then export it to WKT. Wrapper for OSRSetFromUserInput() in the GDAL Spatial Reference System API with output to WKT.

srs_to_projjson() accepts a spatial reference system (SRS) definition in any of the formats supported by srs_to_wkt(), and converts into PROJJSON format. Wrapper for OSRExportToPROJJSON() in the GDAL Spatial Reference System API.

The input SRS may take the following forms:

WKT - to convert WKT versions (see below)
EPSG:n - EPSG code n
AUTO:proj_id,unit_id,lon0,lat0 - WMS auto projections
urn:ogc:def:crs:EPSG::n - OGC URNs
PROJ.4 definitions
filename - file to read for WKT, XML or PROJ.4 definition
well known name such as NAD27, NAD83, WGS84 or WGS72
IGNF:xxxx, ESRI:xxxx - definitions from the PROJ database
PROJJSON (PROJ >= 6.2)

srs_to_wkt() is intended to be flexible, but by its nature it is imprecise as it must guess information about the format intended. epsg_to_wkt() could be used instead for EPSG codes.

As of GDAL 3.0, the default format for WKT export is OGC WKT 1. The WKT version can be overridden by using the OSR_WKT_FORMAT configuration option (see set_config_option()). Valid values are one of: SFSQL, WKT1_SIMPLE, WKT1, WKT1_GDAL, WKT1_ESRI, WKT2_2015, WKT2_2018, WKT2, DEFAULT. If SFSQL, a WKT1 string without AXIS, TOWGS84, AUTHORITY or EXTENSION node is returned. If WKT1_SIMPLE, a WKT1 string without AXIS, AUTHORITY or EXTENSION node is returned. WKT1 is an alias of WKT1_GDAL. WKT2 will default to the latest revision implemented (currently WKT2_2018). WKT2_2019 can be used as an alias of WKT2_2018 since GDAL 3.2

Note

Setting gcs_only = TRUE in srs_to_wkt() is a wrapper of OSRCloneGeogCS() in the GDAL API. The returned WKT will be for the GEOGCS node of the input srs.

Examples

epsg_to_wkt(5070)
#> [1] "PROJCS[\"NAD83 / Conus Albers\",GEOGCS[\"NAD83\",DATUM[\"North_American_Datum_1983\",SPHEROID[\"GRS 1980\",6378137,298.257222101,AUTHORITY[\"EPSG\",\"7019\"]],AUTHORITY[\"EPSG\",\"6269\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.0174532925199433,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\"EPSG\",\"4269\"]],PROJECTION[\"Albers_Conic_Equal_Area\"],PARAMETER[\"latitude_of_center\",23],PARAMETER[\"longitude_of_center\",-96],PARAMETER[\"standard_parallel_1\",29.5],PARAMETER[\"standard_parallel_2\",45.5],PARAMETER[\"false_easting\",0],PARAMETER[\"false_northing\",0],UNIT[\"metre\",1,AUTHORITY[\"EPSG\",\"9001\"]],AXIS[\"Easting\",EAST],AXIS[\"Northing\",NORTH],AUTHORITY[\"EPSG\",\"5070\"]]"
writeLines(epsg_to_wkt(5070, pretty = TRUE))
#> PROJCS["NAD83 / Conus Albers",
#>     GEOGCS["NAD83",
#>         DATUM["North_American_Datum_1983",
#>             SPHEROID["GRS 1980",6378137,298.257222101,
#>                 AUTHORITY["EPSG","7019"]],
#>             AUTHORITY["EPSG","6269"]],
#>         PRIMEM["Greenwich",0,
#>             AUTHORITY["EPSG","8901"]],
#>         UNIT["degree",0.0174532925199433,
#>             AUTHORITY["EPSG","9122"]],
#>         AUTHORITY["EPSG","4269"]],
#>     PROJECTION["Albers_Conic_Equal_Area"],
#>     PARAMETER["latitude_of_center",23],
#>     PARAMETER["longitude_of_center",-96],
#>     PARAMETER["standard_parallel_1",29.5],
#>     PARAMETER["standard_parallel_2",45.5],
#>     PARAMETER["false_easting",0],
#>     PARAMETER["false_northing",0],
#>     UNIT["metre",1,
#>         AUTHORITY["EPSG","9001"]],
#>     AXIS["Easting",EAST],
#>     AXIS["Northing",NORTH],
#>     AUTHORITY["EPSG","5070"]]

srs_to_wkt("NAD83")
#> [1] "GEOGCS[\"NAD83\",DATUM[\"North_American_Datum_1983\",SPHEROID[\"GRS 1980\",6378137,298.257222101,AUTHORITY[\"EPSG\",\"7019\"]],AUTHORITY[\"EPSG\",\"6269\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.0174532925199433,AUTHORITY[\"EPSG\",\"9122\"]],AXIS[\"Latitude\",NORTH],AXIS[\"Longitude\",EAST],AUTHORITY[\"EPSG\",\"4269\"]]"
writeLines(srs_to_wkt("NAD83", pretty = TRUE))
#> GEOGCS["NAD83",
#>     DATUM["North_American_Datum_1983",
#>         SPHEROID["GRS 1980",6378137,298.257222101,
#>             AUTHORITY["EPSG","7019"]],
#>         AUTHORITY["EPSG","6269"]],
#>     PRIMEM["Greenwich",0,
#>         AUTHORITY["EPSG","8901"]],
#>     UNIT["degree",0.0174532925199433,
#>         AUTHORITY["EPSG","9122"]],
#>     AXIS["Latitude",NORTH],
#>     AXIS["Longitude",EAST],
#>     AUTHORITY["EPSG","4269"]]
set_config_option("OSR_WKT_FORMAT", "WKT2")
writeLines(srs_to_wkt("NAD83", pretty = TRUE))
#> GEOGCRS["NAD83",
#>     DATUM["North American Datum 1983",
#>         ELLIPSOID["GRS 1980",6378137,298.257222101,
#>             LENGTHUNIT["metre",1]]],
#>     PRIMEM["Greenwich",0,
#>         ANGLEUNIT["degree",0.0174532925199433]],
#>     CS[ellipsoidal,2],
#>         AXIS["geodetic latitude (Lat)",north,
#>             ORDER[1],
#>             ANGLEUNIT["degree",0.0174532925199433]],
#>         AXIS["geodetic longitude (Lon)",east,
#>             ORDER[2],
#>             ANGLEUNIT["degree",0.0174532925199433]],
#>     ID["EPSG",4269]]
set_config_option("OSR_WKT_FORMAT", "")

srs_to_wkt("EPSG:5070", gcs_only = TRUE)
#> [1] "GEOGCS[\"NAD83\",DATUM[\"North_American_Datum_1983\",SPHEROID[\"GRS 1980\",6378137,298.257222101,AUTHORITY[\"EPSG\",\"7019\"]],AUTHORITY[\"EPSG\",\"6269\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.0174532925199433,AUTHORITY[\"EPSG\",\"9122\"]],AXIS[\"Latitude\",NORTH],AXIS[\"Longitude\",EAST],AUTHORITY[\"EPSG\",\"4269\"]]"

srs_to_projjson("NAD83") |> writeLines()
#> {
#>   "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
#>   "type": "GeographicCRS",
#>   "name": "NAD83",
#>   "datum": {
#>     "type": "GeodeticReferenceFrame",
#>     "name": "North American Datum 1983",
#>     "ellipsoid": {
#>       "name": "GRS 1980",
#>       "semi_major_axis": 6378137,
#>       "inverse_flattening": 298.257222101
#>     }
#>   },
#>   "coordinate_system": {
#>     "subtype": "ellipsoidal",
#>     "axis": [
#>       {
#>         "name": "Geodetic latitude",
#>         "abbreviation": "Lat",
#>         "direction": "north",
#>         "unit": "degree"
#>       },
#>       {
#>         "name": "Geodetic longitude",
#>         "abbreviation": "Lon",
#>         "direction": "east",
#>         "unit": "degree"
#>       }
#>     ]
#>   },
#>   "id": {
#>     "authority": "EPSG",
#>     "code": 4269
#>   }
#> }