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59 lines
2.1 KiB
R
59 lines
2.1 KiB
R
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#' Read a data cube from an existing netCDF file
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#'
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#' Create a proxy data cube from a netCDF file that has been created using \code{\link{write_ncdf}}.
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#' This function does not read cubes from arbitrary netCDF files and can be used e.g., to load intermediate results and/or
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#' plotting existing netCDF cubes on disk without doing the data cube creation from image collections.
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#'
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#' @examples
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#' # create image collection from example Landsat data only
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#' # if not already done in other examples
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#' if (!file.exists(file.path(tempdir(), "L8.db"))) {
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#' L8_files <- list.files(system.file("L8NY18", package = "gdalcubes"),
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#' ".TIF", recursive = TRUE, full.names = TRUE)
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#' create_image_collection(L8_files, "L8_L1TP", file.path(tempdir(), "L8.db"), quiet = TRUE)
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#' }
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#'
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#' L8.col = image_collection(file.path(tempdir(), "L8.db"))
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#' v = cube_view(extent=list(left=388941.2, right=766552.4,
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#' bottom=4345299, top=4744931, t0="2018-04", t1="2018-06"),
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#' srs="EPSG:32618", nx = 497, ny=526, dt="P1M")
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#'
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#' \donttest{
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#' ncfile = write_ncdf(select_bands(raster_cube(L8.col, v), c("B02", "B03", "B04")))
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#' ncdf_cube(ncfile)
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#' }
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#'
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#' @param path path to an existing netCDF file
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#' @param chunking custom chunk sizes to read form the netCDF file; defaults to using chunk sizes from the netCDF file
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#' @param auto_unpack logical; automatically apply offset and scale when reading data values
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#' @return a proxy data cube object
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#' @note This function returns a proxy object, i.e., it will not start any computations besides deriving the shape of the result.
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#' @export
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ncdf_cube <- function(path, chunking = NULL, auto_unpack = TRUE) {
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stopifnot(file.exists(path))
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if (is.null(chunking)) {
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chunking = integer(0)
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}
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x = gc_create_ncdf_cube(path, chunking, auto_unpack)
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class(x) <- c("ncdf_cube", "cube", "xptr")
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return(x)
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}
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is.ncdf_cube <- function(obj) {
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if(!("ncdf_cube" %in% class(obj))) {
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return(FALSE)
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}
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if (gc_is_null(obj)) {
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warning("GDAL data cube proxy object is invalid")
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return(FALSE)
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}
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return(TRUE)
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}
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