compound type and group support

[mdsumner]

Two good examples are

KEA: https://gist.github.com/mdsumner/a65ce8d42edfda5e649c7c4f858303b3#file-kea_rhdf5-r-L6

L3BIN format

https::/github.com/mdsumner/roc

[mdsumner]

Groups without compound types here

u <- "https://www.unidata.ucar.edu/software/netcdf/examples/test_hgroups.nc"
tfile <- file.path(tempdir(), basename(u))
download.file(u, tfile, mode = "wb")

library(tidync)
tidync(tfile)
ncdf4::nc_open(tfile)

All the ncdf4 handling is internal, RNetCDF doesn't support them atm.

[mdsumner]

RNetCDF is planning to support these, but also see h5 and rhdf5.

[mdsumner]

Example with starsdata: https://github.com/r-spatial/stars/issues/54#issuecomment-422262589

[mdsumner]

nHere's a recursive approach to get the group names with RNetCDF 2.0.0

s5p = system.file("sentinel5p/S5P_NRTI_L2__NO2____20180717T120113_20180717T120613_03932_01_010002_20180717T125231.nc", package = "starsdata")
library(RNetCDF)
recurse_ptrs <- function(l, tag) {
  lapply(l, modify_ptr, name = tag)
}

modify_ptr <- function(ptr, name) {
  g <- grp.inq.nc(ptr)
  if (length(g$grps) > 0) recurse_ptrs(g$grps, tag = paste(c(name, g$name), collapse = "/")) else paste(c(name, g$name), collapse = "/")
}
x <- recurse_ptrs(grp.inq.nc(open.nc(s5p))$grps, "")
str(unlist(x))
 chr [1:271] "/PRODUCT/SUPPORT_DATA/GEOLOCATIONS" "/PRODUCT/SUPPORT_DATA/DETAILED_RESULTS" "/PRODUCT/SUPPORT_DATA/INPUT_DATA" ...

grp.inq.nc(open.nc(s5p), unlist(x)[6])
etc. etc. 

[mdsumner]

Ugh, this is not going to be fun. ncdf4 already supports groups, but we don't harvest metadata from ncdf4.

If we can use RNetCDF we can pass in the pointer for the appropriate group, and rewind ahead from nc_meta - but if we have to use ncdf4 we have to write another ncmeta extraction for it. That would be helpful anyway so maybe that.

[mdsumner]

actually looks like it can work, most of the effort will be in ncmeta@groups https://github.com/hypertidy/ncmeta/tree/groups

[mdsumner]

Try this HECRAS stuff https://github.com/mkoohafkan/RAStestR/tree/master/inst/sample-data

[mdsumner]

another example in terra issues #686