[gdal-dev] Making a small(er) test netcdf from a netcdf with subdatasets?

[Kurt Schwehr]

Also asked here:
http://gis.stackexchange.com/questions/170882/how-can-a-make-a-netcdf-with-subgroups-smaller

Is there an easy way to make a netcdf with subdatasets but shrink it
without resorting to C or Fortan?

I'm trying to write a test for code that works with hycom netcdf global
ocean circulation data. The source file 2 subdatasets:

gdalinfo hycom_glb_911_2015110200_t000_uv3z.nc | grep _NAME
  SUBDATASET_1_NAME=NETCDF:"hycom_glb_911_2015110200_t000_uv3z.nc":water_u
  SUBDATASET_2_NAME=NETCDF:"hycom_glb_911_2015110200_t000_uv3z.nc":water_v
With 40 depth bands:

gdalinfo NETCDF:hycom_glb_911_2015110200_t000_uv3z.nc:water_u | grep
'^Band' | head -3
Band 1 Block=4500x1 Type=Int16, ColorInterp=Undefined
Band 2 Block=4500x1 Type=Int16, ColorInterp=Undefined
Band 3 Block=4500x1 Type=Int16, ColorInterp=Undefined
I've got some code written the does things like calculate the speed in m/s
from the UV and creates a geotiff, etc. The original files are much too
large for using in unittests. Is there an easy way with gdal, nco or ? to
keep the structure and metadata, but create a much smaller file? I'm open
to dropping all but the first two bands and writing a constant value into
each band + turning on deflate compression.

Trying with GDAL:

gdal_translate --version  # At head -> r31584
GDAL 2.1.0dev, released 2015/99/99

gdal_translate hycom_glb_911_2015110200_t000_uv3z.nc
hycom_glb_911_2015110200_t000_uv3z-try2.nc -of netcdf -co compress=deflate
Input file contains subdatasets. Please, select one of them for reading.
The originals are quite a bit large for tests:

ls -lh hycom_glb_911_2015110200_t000_uv3z.nc
-rw-r----- 1 schwehr group 1.4G Nov 19 09:13
hycom_glb_911_2015110200_t000_uv3z.nc

Thanks,
-kurt
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