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Transform or convert coordinates of simple feature

Source: R/transform.R, R/proj.R
st_transform.Rd

Transform or convert coordinates of simple feature

Usage

st_can_transform(src, dst)

st_transform(x, crs, ...)

# S3 method for class 'sfc'
st_transform(
  x,
  crs = st_crs(x),
  ...,
  aoi = numeric(0),
  pipeline = character(0),
  reverse = FALSE,
  desired_accuracy = -1,
  allow_ballpark = TRUE,
  partial = TRUE,
  check = FALSE
)

# S3 method for class 'sf'
st_transform(x, crs = st_crs(x), ...)

# S3 method for class 'sfg'
st_transform(x, crs = st_crs(x), ...)

# S3 method for class 'bbox'
st_transform(x, crs, ..., densify = 21)

st_wrap_dateline(x, options, quiet)

# S3 method for class 'sfc'
st_wrap_dateline(x, options = "WRAPDATELINE=YES", quiet = TRUE)

# S3 method for class 'sf'
st_wrap_dateline(x, options = "WRAPDATELINE=YES", quiet = TRUE)

# S3 method for class 'sfg'
st_wrap_dateline(x, options = "WRAPDATELINE=YES", quiet = TRUE)

sf_proj_info(type = "proj", path)

Arguments

src

source crs

dst

destination crs

x

object of class sf, sfc or sfg

crs

target coordinate reference system: object of class crs, or input string for st_crs

...

ignored

aoi

area of interest, in degrees: WestLongitude, SouthLatitude, EastLongitude, NorthLatitude

pipeline

character; coordinate operation pipeline, for overriding the default operation

reverse

boolean; has only an effect when pipeline is defined: if TRUE, the inverse operation of the pipeline is applied

desired_accuracy

numeric; Only coordinate operations that offer an accuracy of at least the one specified will be considered; a negative value disables this feature (requires GDAL >= 3.3)

allow_ballpark

logical; are ballpark (low accuracy) transformations allowed? (requires GDAL >= 3.3)

partial

logical; allow for partial projection, if not all points of a geometry can be projected (corresponds to setting environment variable OGR_ENABLE_PARTIAL_REPROJECTION to TRUE)

check

logical; if TRUE, perform a sanity check on resulting polygons

densify

integer, number of points for discretizing lines between bounding box corner points; see Details

options

character; should have "WRAPDATELINE=YES" to function; another parameter that is used is "DATELINEOFFSET=10" (where 10 is the default value)

quiet

logical; print options after they have been parsed?

type

character; one of have_datum_files, proj, ellps, datum, units, path, or prime_meridians; see Details.

path

character; PROJ search path to be set

Details

st_can_transform returns a boolean indicating whether coordinates with CRS src can be transformed into CRS dst

Transforms coordinates of object to new projection. Features that cannot be transformed are returned as empty geometries. Transforms using the pipeline= argument may fail if there is ambiguity in the axis order of the specified coordinate reference system; if you need the traditional GIS order, use "OGC:CRS84", not "EPSG:4326". Extra care is needed with the ESRI Shapefile format, because WKT1 does not store axis order unambiguously.

The st_transform method for sfg objects assumes that the CRS of the object is available as an attribute of that name.

the method for bbox objects densifies lines for geographic coordinates along Cartesian lines, not great circle arcs

For a discussion of using options, see https://github.com/r-spatial/sf/issues/280 and https://github.com/r-spatial/sf/issues/1983

sf_proj_info lists the available projections, ellipses, datums, units, or data search path of the PROJ library when type is equal to proj, ellps, datum, units or path; when type equals have_datum_files a boolean is returned indicating whether datum files are installed and accessible (checking for conus). path returns the PROJ_INFO.searchpath field directly, as a single string with path separaters (: or ;).

for PROJ >= 6, sf_proj_info does not provide option type = "datums". PROJ < 6 does not provide the option type = "prime_meridians".

for PROJ >= 7.1.0, the "units" query of sf_proj_info returns the to_meter variable as numeric, previous versions return a character vector containing a numeric expression.

See also

st_transform_proj, part of package lwgeom.

sf_project projects a matrix of coordinates, bypassing GDAL altogether

st_break_antimeridian

Examples

p1 = st_point(c(7,52))
p2 = st_point(c(-30,20))
sfc = st_sfc(p1, p2, crs = 4326)
sfc
#> Geometry set for 2 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -30 ymin: 20 xmax: 7 ymax: 52
#> Geodetic CRS:  WGS 84
#> POINT (7 52)
#> POINT (-30 20)
st_transform(sfc, 3857)
#> Geometry set for 2 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -3339585 ymin: 2273031 xmax: 779236.4 ymax: 6800125
#> Projected CRS: WGS 84 / Pseudo-Mercator
#> POINT (779236.4 6800125)
#> POINT (-3339585 2273031)
st_transform(st_sf(a=2:1, geom=sfc), "EPSG:3857")
#> Simple feature collection with 2 features and 1 field
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -3339585 ymin: 2273031 xmax: 779236.4 ymax: 6800125
#> Projected CRS: WGS 84 / Pseudo-Mercator
#>   a                     geom
#> 1 2 POINT (779236.4 6800125)
#> 2 1 POINT (-3339585 2273031)
if (compareVersion(sf_extSoftVersion()["GDAL"], "3.0.0") >= 0) {
  st_transform(sfc, pipeline =
    "+proj=pipeline +step +proj=axisswap +order=2,1") # reverse axes
  st_transform(sfc, pipeline =
    "+proj=pipeline +step +proj=axisswap +order=2,1", reverse = TRUE) # also reverse axes
}
#> Geometry set for 2 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -30 ymin: 20 xmax: 7 ymax: 52
#> CRS:           NA
#> POINT (7 52)
#> POINT (-30 20)
nc = st_read(system.file("shape/nc.shp", package="sf"))
#> Reading layer `nc' from data source 
#>   `/home/runner/work/_temp/Library/sf/shape/nc.shp' using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27
st_area(nc[1,]) # area from long/lat
#> 1137107793 [m^2]
st_area(st_transform(nc[1,], 32119)) # NC state plane, m
#> 1137590142 [m^2]
st_area(st_transform(nc[1,], 2264)) # NC state plane, US foot
#> 12244869403 [US_survey_foot^2]
library(units)
#> udunits database from /usr/share/xml/udunits/udunits2.xml
set_units(st_area(st_transform(nc[1,], 2264)), m^2)
#> 1137590142 [m^2]
st_transform(structure(p1, proj4string = "EPSG:4326"), "EPSG:3857")
#> POINT (779236.4 6800125)
st_wrap_dateline(st_sfc(st_linestring(rbind(c(-179,0),c(179,0))), crs = 4326))
#> Geometry set for 1 feature 
#> Geometry type: MULTILINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: -180 ymin: 0 xmax: 180 ymax: 0
#> Geodetic CRS:  WGS 84
#> MULTILINESTRING ((-179 0, -180 0), (180 0, 179 0))
sf_proj_info("datum")
#> data frame with 0 columns and 0 rows