st_crop function

crop a stars object

## S3 method for class 'mdim'
st_crop(x, y, ...)

## S3 method for class 'stars_proxy'
st_crop(
  x,
  y,
  ...,
  crop = TRUE,
  epsilon = sqrt(.Machine$double.eps),
  collect = TRUE
)

## S3 method for class 'stars'
st_crop(
  x,
  y,
  ...,
  crop = TRUE,
  epsilon = sqrt(.Machine$double.eps),
  as_points = all(st_dimension(y) == 2, na.rm = TRUE),
  normalize = FALSE
)

Arguments

• x: object of class stars
• y: object of class sf, sfc or bbox; see Details below.
• ...: ignored
• crop: logical; if TRUE, the spatial extent of the returned object is cropped to still cover obj, if FALSE, the extent remains the same but cells outside y are given NA values.
• epsilon: numeric; factor to shrink the bounding box of y towards its center before cropping.
• collect: logical; if TRUE, repeat cropping on stars object, i.e. after data has been read
• as_points: logical; only relevant if y is of class sf or sfc: if FALSE, treat x as a set of points, else as a set of small polygons. Default: TRUE if y is two-dimensional, else FALSE; see Details
• normalize: logical; if TRUE then pass the cropped object to st_normalize before returning. This typically changes the offset field and resets the from field to 1, and changes the bounding box of the returned object accordingly.

Details

for raster x, st_crop selects cells that intersect with y. For intersection, are raster cells interpreted as points or as small polygons? If y is of class stars, x raster cells are interpreted as points; if y is of class bbox, x cells are interpreted as cells (small polygons). Otherwise, if as_points is not given, cells are interpreted as points if y has a two-dimensional geometry.

Examples

l7 = read_stars(system.file("tif/L7_ETMs.tif", package = "stars"))
d = st_dimensions(l7)

# area around cells 3:10 (x) and 4:11 (y):
offset = c(d[["x"]]$offset, d[["y"]]$offset)
res = c(d[["x"]]$delta, d[["y"]]$delta)
bb = st_bbox(c(xmin = offset[1] + 2 * res[1],
        ymin = offset[2] + 11 * res[2],
        xmax = offset[1] + 10 * res[1],
        ymax = offset[2] +  3 * res[2]), crs = st_crs(l7))
l7[bb]
# equivalent:
st_crop(l7, bb)

plot(l7[,1:13,1:13,1], reset = FALSE)
image(l7[bb,,,1], add = TRUE, col = sf.colors())
plot(st_as_sfc(bb), add = TRUE, border = 'green', lwd = 2)

# slightly smaller bbox:
bb = st_bbox(c(xmin = offset[1] + 2.1 * res[1],
        ymin = offset[2] + 10.9 * res[2],
        xmax = offset[1] +  9.9 * res[1],
        ymax = offset[2] +  3.1 * res[2]), crs = st_crs(l7))
l7[bb]

plot(l7[,1:13,1:13,1], reset = FALSE)
image(l7[bb,,,1], add = TRUE, col = sf.colors())
plot(st_as_sfc(bb), add = TRUE, border = 'green', lwd = 2)

# slightly larger bbox:
bb = st_bbox(c(xmin = offset[1] + 1.9 * res[1],
        ymin = offset[2] + 11.1 * res[2],
        xmax = offset[1] + 10.1 * res[1],
        ymax = offset[2] +  2.9 * res[2]), crs = st_crs(l7))
l7[bb]

plot(l7[,1:13,1:13,1], reset = FALSE)
image(l7[bb,,,1], add = TRUE, col = sf.colors())
plot(st_as_sfc(bb), add = TRUE, border = 'green', lwd = 2)

# half a cell size larger bbox:
bb = st_bbox(c(xmin = offset[1] + 1.49 * res[1],
        ymin = offset[2] + 11.51 * res[2],
        xmax = offset[1] + 10.51 * res[1],
        ymax = offset[2] +  2.49 * res[2]), crs = st_crs(l7))
l7[bb]

plot(l7[,1:13,1:13,1], reset = FALSE)
image(l7[bb,,,1], add = TRUE, col = sf.colors())
plot(st_as_sfc(bb), add = TRUE, border = 'green', lwd = 2)