add -z (e.g. -z5) compression option to ahi2cmi

results in ~964M B03 going down to ~164M

himawari/ahi2cmi.py

@@ -482,7 +482,7 @@ class HimawariAHIasCMIP(object):
         bwl = np.array([bwl_um], dtype=np.float32)
         yield self.p('band_id'), band, self.d(DEFAULT_BAND_DIM_NAME), a
 
-    def walk(self):
+    def walk(self, extra_data_attrs={}):
         """
         iterate PVDA frames equivalent to a PUG nc_walk
         """
@@ -509,7 +509,8 @@ class HimawariAHIasCMIP(object):
         # we almost forgot! the data itself
         v = self.data
         d = self.data_dims
-        a = self.data_attrs
+        a = dict(self.data_attrs)
+        a.update(extra_data_attrs)
         yield self.p(self._data_name), v, d, a
 
     #
@@ -680,16 +681,20 @@ class tests(unittest.TestCase):
             n_frames += 1
         print("%d frames" % n_frames)
 
-def write_netcdf(path, as_radiances=False, filename_format="{}.nc"):
+def write_netcdf(path, as_radiances=False, filename_format="{}.nc", complevel=None):
     from goesr.rockfall import rename, nc_write, autoscale
     fnstem = os.path.splitext(os.path.split(path)[-1])[0]
     fn = filename_format.format(fnstem)
     pathout = os.path.abspath(fn)
     lething = HimawariAHIasCMIP(path, as_radiances=as_radiances)
     varname = DEFAULT_CMIP_RAD_NAME if as_radiances else DEFAULT_CMIP_NAME
+    extra_data_attrs = {}
+    if complevel:
+        extra_data_attrs['.complevel'] = complevel if isinstance(complevel, int) else 7
+        extra_data_attrs['.zlib'] = True
     for fnwrit in nc_write(
                             rename(
-                                autoscale( lething.walk(),
+                                autoscale( lething.walk(extra_data_attrs=extra_data_attrs),
                                     variable_names_matching={varname}
                                 ),
                                 pathout
@@ -721,6 +726,8 @@ def main():
                         help='each occurrence increases verbosity 1 level through ERROR-WARNING-INFO-DEBUG')
     parser.add_argument('-d', '--debug', dest='debug', action='store_true',
                         help="enable interactive PDB debugger on exception")
+    parser.add_argument('-z', '--compress', dest='compress', type=int, default=0,
+                        help='set compression level 0..9 for image data variable')
     parser.add_argument('inputs', nargs='*',
                         help="input files to process")
     args = parser.parse_args()
@@ -736,7 +743,7 @@ def main():
         return 0
 
     for pn in args.inputs:
-        write_netcdf(pn, args.rad, "{}_rad.nc" if args.rad else "{}_cmi.nc")
+        write_netcdf(pn, args.rad, "{}_rad.nc" if args.rad else "{}_cmi.nc", complevel=args.compress)
 
     return 0