Cast to one GeoArrow geometry type

Each of these casts to the single type its name gives. Because the result type does not depend on the data, these are the casts Arrow can run inside a query, which ga_from_wkb() cannot.

Usage

ga_as_point(x)

ga_as_linestring(x)

ga_as_polygon(x)

ga_as_multipoint(x)

ga_as_multilinestring(x)

ga_as_multipolygon(x)

Arguments

x

a binary array of WKB, or any GeoArrow array

Value

a GeoArrow array of the named type, the same length as x

Details

Parsing WKB is the expensive part of using a plain Parquet geometry column, and every function that needs a concrete geometry type pays for it on its own. Casting once up front means the rest of the query runs on native GeoArrow instead:

trip |>
  mutate(pickup = ga_as_point(t_pickuploc)) |>
  mutate(
    d = ga_dist_euclidean_pairwise(pickup, dropoff),
    b = ga_bearing_euclidean(pickup, dropoff)
  )

The cast is fallible. A geometry that does not fit the target type, such as a two point multipoint cast to point, is an error rather than a null.

See also

Other cast: ga_cast_geometry(), ga_downcast_geometry(), ga_explode(), ga_flatten(), ga_from_wkb()

Examples

sfc <- sf::st_sfc(sf::st_point(c(0, 0)), sf::st_point(c(3, 4)))
wkb <- nanoarrow::as_nanoarrow_array(
  arrow::Array$create(unclass(wk::as_wkb(sfc)), type = arrow::binary())
)

pts <- ga_as_point(wkb)
sf::st_as_sfc(geoarrow::as_geoarrow_vctr(pts))
#> Geometry set for 2 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 0 xmax: 3 ymax: 4
#> CRS:           NA
#> POINT (0 0)
#> POINT (3 4)