## a manifest array in a virtual Zarr store contains references like this (for this file it is >90000 references
## because 28x51*1500x3600 in 1x1x300x300 blocks)
#'1.39.0.7': {'path': 'https://thredds.nci.org.au/thredds/fileServer/gb6/BRAN/BRAN2020/daily/ocean_salt_1993_01.nc',
# 'offset': 302129687, 'length': 48186},
## so let's unpack one block
path <- "https://thredds.nci.org.au/thredds/fileServer/gb6/BRAN/BRAN2020/daily/ocean_salt_1993_01.nc"
library(gdalraster)
## we could use generic url connections but I'm not sure how to do that, GDAL VSIFile makes it easy
vsi <- new(VSIFile, sprintf("/vsicurl/%s", path))
vsi$rewind() ## ensure we are at start of file, then seek to the offset
vsi$seek(302129687, SEEK_SET)
cmp_bytes <- vsi$read(48186)
## decompress the bytes
bytes <- memDecompress(cmp_bytes, "gzip")
length(bytes) ## 1x1x300x300 (*2)
## rearrange because they were shuffled
bytes <- c(t(matrix(bytes, ncol = 2))) ## "shuffle"
## unpack the 2-byte integers
vals <- readBin(bytes, what = "integer", size = 2L, signed = T, n = 300 * 300, endian = "little")
vals[vals == -32768] <- NA
## make a picture
image(matrix(vals, 300))
