Obtain information about a spatial reference system

Bindings to a subset of the GDAL Spatial Reference System API (https://gdal.org/en/stable/api/ogr_srs_api.html). These functions return various information about a spatial reference system passed as text in any of the formats supported by srs_to_wkt().

Usage

srs_get_name(srs)

srs_find_epsg(srs, all_matches = FALSE)

srs_is_geographic(srs)

srs_is_derived_gcs(srs)

srs_is_local(srs)

srs_is_projected(srs)

srs_is_compound(srs)

srs_is_geocentric(srs)

srs_is_vertical(srs)

srs_is_dynamic(srs)

srs_is_same(
  srs,
  srs_other,
  criterion = "",
  ignore_axis_mapping = FALSE,
  ignore_coord_epoch = FALSE
)

srs_get_angular_units(srs)

srs_get_linear_units(srs)

srs_get_coord_epoch(srs)

srs_get_utm_zone(srs)

srs_get_axis_mapping_strategy(srs)

Arguments

srs: Character string containing an SRS definition in various formats (e.g., WKT, PROJ.4 string, well known name such as NAD27, NAD83, WGS84, etc., see srs_to_wkt()).
all_matches: Logical scalar. TRUE to return all identified matches in a data frame, including a confidence value (0-100) for each match. The default is FALSE which returns a character string in the form "EPSG:<code>" for the first match (highest confidence).
srs_other: Character string containing an SRS definition in various formats(see above).
criterion: Character string. One of STRICT, EQUIVALENT, EQUIVALENT_EXCEPT_AXIS_ORDER_GEOGCRS. Defaults to EQUIVALENT_EXCEPT_AXIS_ORDER_GEOGCRS.
ignore_axis_mapping: Logical scalar. If TRUE, sets IGNORE_DATA_AXIS_TO_SRS_AXIS_MAPPING=YES in the call to OSRIsSameEx() in the GDAL Spatial Reference System API. Defaults to NO.
ignore_coord_epoch: Logical scalar. If TRUE, sets IGNORE_COORDINATE_EPOCH=YES in the call to OSRIsSameEx() in the GDAL Spatial Reference System API. Defaults to NO.

Details

srs_find_epsg() tries to find a matching EPSG code. Matching may be partial, or may fail. If all_matches = TRUE, returns a data frame with entries sorted by decreasing match confidence (first entry has the highest match confidence); the default is FALSE which returns a character string in the form "EPSG:####" for the first match (highest confidence). Wrapper of OSRFindMatches() in the GDAL SRS API.

srs_get_name() returns the SRS name. Wrapper of OSRGetName() in the GDAL API.

srs_is_geographic() returns TRUE if the root is a GEOGCS node. Wrapper of OSRIsGeographic() in the GDAL API.

srs_is_derived_gcs() returns TRUE if the SRS is a derived geographic coordinate system (for example a rotated long/lat grid). Wrapper of OSRIsDerivedGeographic() in the GDAL API.

srs_is_local() returns TRUE if the SRS is a local coordinate system (the root is a LOCAL_CS node). Wrapper of OSRIsLocal() in the GDAL API.

srs_is_projected() returns TRUE if the SRS contains a PROJCS node indicating a it is a projected coordinate system. Wrapper of OSRIsProjected() in the GDAL API.

srs_is_compound() returns TRUE if the SRS is compound. Wrapper of OSRIsCompound() in the GDAL API.

srs_is_geocentric() returns TRUE if the SRS is a geocentric coordinate system. Wrapper of OSRIsGeocentric() in the GDAL API.

srs_is_vertical() returns TRUE if the SRS is a vertical coordinate system. Wrapper of OSRIsVertical() in the GDAL API.

srs_is_dynamic() returns TRUE if the SRS is is a dynamic coordinate system (relies on a dynamic datum, i.e., a datum that is not plate-fixed). Wrapper of OSRIsDynamic() in the GDAL API. Requires GDAL >= 3.4.

srs_is_same() returns TRUE if two spatial references describe the same system. Wrapper of OSRIsSame() in the GDAL API.

srs_get_angular_units() fetches the angular geographic coordinate system units. Returns a list of length two: the first element contains the unit name as a character string, and the second element contains a numeric value to multiply by angular distances to transform them to radians. Wrapper of OSRGetAngularUnits() in the GDAL API.

srs_get_linear_units() fetches the linear projection units. Returns a list of length two: the first element contains the unit name as a character string, and the second element contains a numeric value to multiply by linear distances to transform them to meters. If no units are available, values of "Meters" and 1.0 will be assumed. Wrapper of OSRGetLinearUnits() in the GDAL API.

srs_get_coord_epoch() returns the coordinate epoch, as decimal year (e.g. 2021.3), or 0 if not set or not relevant. Wrapper of OSRGetCoordinateEpoch() in the GDAL API. Requires GDAL >= 3.4.

srs_get_utm_zone() returns the UTM zone number or zero if srs isn't a UTM definition. A positive value indicates northern hemisphere; a negative value is in the southern hemisphere. Wrapper of OSRGetUTMZone() in the GDAL API.

srs_get_axis_mapping_strategy() returns the data axis to CRS axis mapping strategy as a character string, one of:

OAMS_TRADITIONAL_GIS_ORDER: for geographic CRS with lat/long order, the data will still be long/lat ordered. Similarly for a projected CRS with northing/easting order, the data will still be easting/northing ordered.
OAMS_AUTHORITY_COMPLIANT: the data axis will be identical to the CRS axis.
OAMS_CUSTOM: custom-defined data axis

Examples

wkt <- 'PROJCS["ETRS89 / UTM zone 32N (N-E)",
        GEOGCS["ETRS89",
            DATUM["European_Terrestrial_Reference_System_1989",
                SPHEROID["GRS 1980",6378137,298.257222101,
                    AUTHORITY["EPSG","7019"]],
                TOWGS84[0,0,0,0,0,0,0],
                AUTHORITY["EPSG","6258"]],
            PRIMEM["Greenwich",0,
                AUTHORITY["EPSG","8901"]],
            UNIT["degree",0.0174532925199433,
                AUTHORITY["EPSG","9122"]],
            AUTHORITY["EPSG","4258"]],
        PROJECTION["Transverse_Mercator"],
        PARAMETER["latitude_of_origin",0],
        PARAMETER["central_meridian",9],
        PARAMETER["scale_factor",0.9996],
        PARAMETER["false_easting",500000],
        PARAMETER["false_northing",0],
        UNIT["metre",1,
            AUTHORITY["EPSG","9001"]],
        AXIS["Northing",NORTH],
        AXIS["Easting",EAST]]'

srs_find_epsg(wkt)
#> [1] "EPSG:3044"

srs_find_epsg(wkt, all_matches = TRUE)
#>   authority_name authority_code confidence
#> 1           EPSG           3044        100

srs_get_name("EPSG:5070")
#> [1] "NAD83 / Conus Albers"

srs_is_geographic("EPSG:5070")
#> [1] FALSE
srs_is_geographic("EPSG:4326")
#> [1] TRUE

srs_is_derived_gcs("WGS84")
#> [1] FALSE

srs_is_projected("EPSG:5070")
#> [1] TRUE
srs_is_projected("EPSG:4326")
#> [1] FALSE

srs_is_compound("EPSG:4326")
#> [1] FALSE

srs_is_geocentric("EPSG:7789")
#> [1] TRUE

srs_is_vertical("EPSG:5705")
#> [1] TRUE

f <- system.file("extdata/storml_elev.tif", package="gdalraster")
ds <- new(GDALRaster, f)

ds$getProjection() |> srs_is_projected()
#> [1] TRUE
ds$getProjection() |> srs_get_utm_zone()
#> [1] 12
ds$getProjection() |> srs_get_angular_units()
#> $unit_name
#> [1] "degree"
#> 
#> $to_radians
#> [1] 0.01745329
#> 
ds$getProjection() |> srs_get_linear_units()
#> $unit_name
#> [1] "metre"
#> 
#> $to_meters
#> [1] 1
#> 
ds$getProjection() |> srs_get_axis_mapping_strategy()
#> [1] "OAMS_AUTHORITY_COMPLIANT"

ds$getProjection() |> srs_is_same("EPSG:26912")
#> [1] TRUE
ds$getProjection() |> srs_is_same("NAD83")
#> [1] FALSE

ds$close()

# Requires GDAL >= 3.4
if (as.integer(gdal_version()[2]) >= 3040000) {
  if (srs_is_dynamic("WGS84"))
    print("WGS84 is dynamic")

  if (!srs_is_dynamic("NAD83"))
    print("NAD83 is not dynamic")
}
#> [1] "WGS84 is dynamic"
#> [1] "NAD83 is not dynamic"

Obtain information about a spatial reference system

Usage

Arguments

Details

See also

Examples