Mask a streamed raster to a polygon layer

Keeps the pixels of a .vec raster whose cell centre falls inside a resident polygon layer and sets the rest to background, reading the raster one tile-row strip at a time so the whole grid is never resident. It is the raster counterpart of spatial_clip(): the streamed side is the (large) raster and the small mask layer stays in memory. With inverse = TRUE the inside is cleared and the outside kept.

Usage

mask(
  x,
  mask,
  inverse = FALSE,
  band = NULL,
  background = NA_real_,
  path = NULL,
  dtype = "f32",
  compression = c("fast", "balanced", "max")
)

Arguments

x: A vectra_raster (from vec_open_raster()) or a path to a .vec raster.
mask: An sf or sfc polygon layer to clip against. When it carries no CRS it inherits the raster's EPSG.
inverse: If FALSE (default) keep pixels inside mask; if TRUE keep the pixels outside it.
band: Band(s) to mask (1-based). Default NULL masks every band.
background: Value written to cleared pixels. Default NA_real_.
path: Optional output .vec path. When given the result is streamed to disk and the opened vec_open_raster() handle is returned invisibly; when NULL the result is returned in memory (a matrix for one band, a list of matrices for several).
dtype: Storage dtype for .vec output (see vec_write_raster()). Default "f32".
compression: Compression effort for .vec output. Default "fast".

Value

When path is NULL, a numeric matrix (one band) or a list of matrices (several), each carrying gt, extent, and crs attributes (row 1 northmost). When path is given, the written vectra_raster handle (invisibly).

Details

This is the monoid fold tier of the spatial toolbox: bounded to one strip plus the resident mask, a single streaming pass, no spill. A pixel is tested against the mask only when its centre falls in the mask bounding box, so the point-in-polygon work stays proportional to the overlap rather than the whole grid. Point-in-polygon is delegated to sf (an optional dependency); topology and CRS handling are sf's.

Examples

vals <- matrix(1:100, 10, 10, byrow = TRUE)
f <- tempfile(fileext = ".vec")
vec_write_raster(vals, f, dtype = "f64", extent = c(0, 0, 10, 10))

disc <- sf::st_buffer(sf::st_sfc(sf::st_point(c(5, 5))), 3)
inside <- mask(f, disc)
sum(!is.na(inside))
unlink(f)