Seth-
Thanks very much for the information and pointer to the ticket
documenting the issue!
Do you know if NaN is an allowed value for actual_range? In our
historical data, a variable is retained if it was collected, even though
the sensor failed completely (and all the data was replaced by
_FillValue). In this case, actual_range would be [NaN NaN] for that
variable.
I appreciate the help!
Ellyn
On 05/22/2013 05:04 PM, Seth McGinnis wrote:
Hi Ellyn,
According to CF Trac Ticket #31 (slated for inclusion in the update to CF 1.7),
the way to cache minimum & maximum values in metadata is to use an attribute
named "actual_range" and store them as a pair.
(I kind of think this is a bad idea, and wish that ticket was still open. I
missed this discussion when it happened, but my experience with actual_max type
attributes in practice has convinced me that it's SO easy for them to become
inconsistent that it would really be better not to include them at all.
Computing the min & max on the fly is cheap, and approximating it is even
cheaper, so why introduce the uncertainty? But if they do need to go into
metadata, I think it would be better to use a name that highlighted the fact
that they're potentially unreliable. Maybe something like "nominal_range"
rather than "actual_range"?)
Anyway, the details on how actual_range works can be found here:
https://cf-pcmdi.llnl.gov/trac/ticket/31
Cheers,
--Seth
The second part of the question involves variable attributes we now call
minimum and maximum. Do these names have special meanings? In our files, we
include the actual minimum and maximum computed for each non-coordinate
variable's data. I want to be clear about the content of these attributes,
and wonder if others use different terms to avoid confusion with valid_min and
valid_max? Would calling these attributes "computed_minimum" (maximum) or
"actual_minimum" (maximum) be better?
Thanks for any suggestions!
Ellyn
--
Ellyn T. Montgomery, Oceanographer and Data Manager
U.S. Geological Survey
Woods Hole Coastal and Marine Science Center
384 Woods Hole Road, Woods Hole, MA 02543-1598
(508)457-2356
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