st_as_sf function

Convert stars object into an sf object

## S3 method for class 'stars'
st_as_sfc(x, ..., as_points, which = seq_len(prod(dim(x)[1:2])))

## S3 method for class 'stars'
st_as_sf(
  x,
  ...,
  as_points = FALSE,
  merge = FALSE,
  na.rm = TRUE,
  use_integer = is.logical(x[[1]]) || is.integer(x[[1]]),
  long = FALSE,
  connect8 = FALSE
)

## S3 method for class 'stars_proxy'
st_as_sf(x, ..., downsample = 0)

Arguments

• x: object of class stars
• ...: ignored
• as_points: logical; should cells be converted to points or to polygons? See details.
• which: linear index of cells to keep (this argument is not recommended to be used)
• merge: logical; if TRUE, cells with identical values are merged (using GDAL_Polygonize or GDAL_FPolygonize); if FALSE, a polygon for each raster cell is returned; see details
• na.rm: logical; should missing valued cells be removed, or also be converted to features?
• use_integer: (relevant only if merge is TRUE): if TRUE, before polygonizing values are rounded to 32-bits signed integer values (GDALPolygonize), otherwise they are converted to 32-bit floating point values (GDALFPolygonize).
• long: logical; if TRUE, return a long table form sf, with geometries and other dimensions recycled
• connect8: logical; if TRUE, use 8 connectedness. Otherwise the 4 connectedness algorithm will be applied.
• downsample: see st_as_stars

Details

If merge is TRUE, only the first attribute is converted into an sf object. If na.rm is FALSE, areas with NA values are also written out as polygons. Note that the resulting polygons are typically invalid, and use st_make_valid to create valid polygons out of them.

Examples

tif = system.file("tif/L7_ETMs.tif", package = "stars")
x = read_stars(tif)
x = x[,1:100,1:100,6] # subset of a band with lower values in it
x[[1]][x[[1]] < 30] = NA # set lower values to NA
x[[1]] = x[[1]] < 100 # make the rest binary
x
(p = st_as_sf(x)) # removes NA areas
(p = st_as_sf(x[,,,1], merge = TRUE)) # glues polygons together
all(st_is_valid(p)) # not all valid, see details
plot(p, axes = TRUE)
(p = st_as_sf(x, na.rm = FALSE, merge = TRUE)) # includes polygons with NA values
plot(p, axes = TRUE)