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--- fimex:usage [2022-05-31 09:29:32]
external edit
+++ fimex:usage [2022-11-15 14:13:54] (current)
alexanderb change wording
@@ Line 1: / Line 1: @@
-====== Usage Example ======
+====== Usage Examples ======
 ===== Converting a felt model output from felt to NetCDF =====
@@ Line 9: / Line 9: @@
   - adjust the projection and area you want to extract in fimex_example.cfg (or use command line arguments to fimex)
   - run <code>fimex -c fimex_example.cfg</code>
+===== Writing zarr with libnetcdf =====
+Zarr does not support unlimited dimensions. You may need to set ''unlimited=false'' for some dimensions, e.g. with ncml like
+  <?xml version="1.0" encoding="UTF-8"?>
+  <netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2"
+          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+    <dimension name="time" length="61" isUnlimited="false" />
+  </netcdf>
+In version 4.8.1, libnetcdf does not support compressed zarr chunks. You probably have to disable compression with a netcdf writer config xml file similar to:
+  <?xml version="1.0" encoding="UTF-8"?>
+  <cdm_ncwriter_config>
+    <default compressionLevel="0" />
+  </cdm_ncwriter_config>
+The fimex command would then be something like
+  fimex \
+      --input.file "input.nc" \
+      --input.config "no_unlimited_dim.ncml" \
+      --output.file "file:///path/to/output#mode=nczarr,file" \
+      --output.config "nc_writer_no_compression.xml" \
+      --output.type nc4
+Please note that using libnetcdf to write zarr will still use a lock on libnetcdf function calls, i.e. there will only be one thread at a time reading or writing.
+Datasets that were written like this do not seem to be readable with the same url (observed with netcdf 4.8.1), but reading appears to work with ''mode=zarr,file'' (i.e., not ''nczarr'').
+See the [[https://docs.unidata.ucar.edu/nug/current/nczarr_head.html|libnetcdf zarr documentation]] for more details on zarr support in libnetcdf.