Hello Jim, Julien,
I'm not sure .. I think the conformance might be right here and your flag_values should be 0,1,2,3, 4, 8,12,16, and flag_masks 3,3,3,3,28,28,28,28
If, for instance, you very_bad_quality and very_bad_weather, then "var" should have value 4 = '00100000` in binary. Masked with 3 (11000000) gives zero, and masked with 28 (00111000) gives 4. Re-using the zero value would make zero ambiguous, so you need to start the 2nd sequence at 4.
regards,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jim Biard <jbiard at cicsnc.org>
Sent: 20 November 2018 16:51:24
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Multiple zeros in flag_values allowed?
Julien,
That's fine. The conformance document probably needs a better statement of the requirement when flag masks are used.
Grace and peace,
Jim
On 11/20/18 11:40 AM, Julien Demaria wrote:
Hi,
We want to define a flags variable defining like that:
var:flag_masks = 3, 3, 3, 3, 12, 12, 12, 12 ;
var:flag_values = 0, 1, 2, 3, 0, 4, 8, 12 ;
var:flag_meanings = ?very_bad_quality bad_quality good_quality very_good_quality
very_bad_weather bad_weather good_weather very_good_weather? ;
I understand from
http://cfconventions.org/Conformance/conformance.html that it is not allowed to use several time the same value (here zero) in flag_values:
Requirements:
? The flag_values attribute values must be mutually exclusive among the set of flag_values attribute values defined for that variable.
So it means that for each new ?bits combination? in the flags definition we lost one of the combination because we cannot use zero more than one time?
Do you confirm this? What is the reason?
Thanks in advance,
Julien
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Received on Wed Nov 21 2018 - 10:03:29 GMT
