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Apply a coordinate transformation to a WKB/WKT geometry

Source: R/geom.R
g_transform.Rd

g_transform() will transform the coordinates of a geometry from their current spatial reference system to a new target spatial reference system. Normally this means reprojecting the vectors, but it could include datum shifts, and changes of units.

Usage

g_transform(
  geom,
  srs_from,
  srs_to,
  wrap_date_line = FALSE,
  date_line_offset = 10L,
  traditional_gis_order = TRUE,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

Arguments

geom

Either a raw vector of WKB or list of raw vectors, or a character vector containing one or more WKT strings.

srs_from

Character string specifying the spatial reference system for geom. May be in WKT format or any of the formats supported by srs_to_wkt().

srs_to

Character string specifying the output spatial reference system. May be in WKT format or any of the formats supported by srs_to_wkt().

wrap_date_line

Logical value, TRUE to correct geometries that incorrectly go from a longitude on a side of the antimeridian to the other side. Defaults to FALSE.

date_line_offset

Integer longitude gap in degree. Defaults to 10L.

traditional_gis_order

Logical value, TRUE to use traditional GIS order of axis mapping (the default) or FALSE to use authority compliant axis order. By default, input geom vertices are assumed to be in longitude/latitude order if srs_from is a geographic coordinate system. This can be overridden by setting traditional_gis_order = FALSE.

as_wkb

Logical value, TRUE to return the output geometry in WKB format (the default), or FALSE to return as WKT.

as_iso

Logical value, TRUE to export as ISO WKB/WKT (ISO 13249 SQL/MM Part 3), or FALSE (the default) to export as "Extended WKB/WKT".

byte_order

Character string specifying the byte order when output is WKB. One of "LSB" (the default) or "MSB" (uncommon).

quiet

Logical value, TRUE to suppress warnings. Defaults to FALSE.

Value

A geometry as WKB raw vector or WKT string, or a list/character vector of geometries as WKB/WKT with length equal to the number of input geometries. NA is returned with a warning if WKB input cannot be converted into an OGR geometry object, or if an error occurs in the call to the underlying OGR API.

Note

This function uses the OGR_GeomTransformer_Create() and OGR_GeomTransformer_Transform() functions in the GDAL API: "This is an enhanced version of OGR_G_Transform(). When reprojecting geometries from a Polar Stereographic projection or a projection naturally crossing the antimeridian (like UTM Zone 60) to a geographic CRS, it will cut geometries along the antimeridian. So a LineString might be returned as a MultiLineString."

The wrap_date_line = TRUE option might be specified for circumstances to correct geometries that incorrectly go from a longitude on a side of the antimeridian to the other side, e.g., LINESTRING (-179 0,179 0) will be transformed to MULTILINESTRING ((-179 0,-180 0),(180 0,179 0)). For that use case, srs_to might be the same as srs_from.

See also

bbox_transform(), transform_bounds()

Examples

pt <- "POINT (-114.0 47.0)"
g_transform(pt, "WGS84", "EPSG:5070", as_wkb = FALSE)
#> [1] "POINT (-1367125.77866242 2797551.11860518)"

# correct geometries that incorrectly go from a longitude on a side of the
# antimeridian to the other side
geom <- "LINESTRING (-179 0,179 0)"
g_transform(geom, "WGS84", "WGS84", wrap_date_line = TRUE, as_wkb = FALSE)
#> [1] "MULTILINESTRING ((-179 0,-180 0),(180 0,179 0))"