Hi folks,
I was hoping someone can clarify for me the correct use of the valid_min,
valid_max and valid_range attributes by *well-behaved* netCDF clients.
Given the netCDF file shown below (in CDL form), and considering the rules for
handling the aforementioned attributes, as defined in Appendix A of the NetCDF
user guide (see
http://www.unidata.ucar.edu/software/netcdf/docs/attribute_conventions.html), I
*think* I'd expect conforming netCDF clients to represent the data for each of
the variables var1..var3 as an array with values (_, -272, 0, 100, 9999, _),
where _ signifies missing data values.
---
netcdf mditest {
dimensions:
dim1 = 6;
variables:
float var1(dim1);
var1:long_name = "var1";
var1:units = "1";
var1:valid_min = -273.0f;
var1:valid_max = 1.0e5f;
float var2(dim1);
var2:long_name = "var2";
var2:units = "1";
var2:valid_min = -273.0f;
var2:_FillValue = 1.0e5f; // constrains valid_max
float var3(dim1);
var3:long_name = "var3";
var3:units = "1";
var3:_FillValue = -273.0f; // constrains valid_min
var3:valid_max = 1.0e5f;
// global attributes
:Conventions = "CF-1.0";
data:
var1 = -300, -272, 0, 100, 9999, 1e6 ;
var2 = -300, -272, 0, 100, 9999, 1e6 ;
var3 = -300, -272, 0, 100, 9999, 1e6 ;
}
---
However, having tried several different netCDF clients - some C, some Java,
some Python - none of them appear to adhere consistently to the aforementioned
rules for handling the valid min/max/range attributes. The python-based
clients, in particular, only seem to honour the _FillValue attribute,
reflecting, I believe, the current behaviour of the netcdf4-python module.
Am I perhaps misinterpreting the nc attribute-handling conventions?
Regards,
--
Phil Bentley PhD, Climate Science IT Apps Group
Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, United Kingdom
Tel: +44 (0)1392 886881
Email: philip.bentley@xxxxxxxxxxxxxxxx Web: http://www.metoffice.gov.uk/
