[CF-metadata] attributes for min/max data valuesfor visualization

[Pascoe, S (Stephen)]

Since Jon mentions me in this thread I'll put in my brief contribution,
although I agree very much with the discussion so far.

Despite the limitations I think we really need these attributes.  At
BADC we are either putting custom attributes in the NetCDF or setting
approximate min/max in configuration files.  A standard approach would
be a great improvement.

I too like actual_min/max.

Cheers,
Stephen.

---
Stephen Pascoe  +44 (0)1235 445980
British Atmospheric Data Centre
Rutherford Appleton Laboratory

-----Original Message-----
From: cf-metadata-bounces at cgd.ucar.edu
[mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of John Caron
Sent: 10 June 2008 00:54
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] attributes for min/max data valuesfor
visualization

I also like "actual_min" and "actual_max": short and to the point.

One point Ill make is that I see a number of well thought out files
using valid_min and valid_max when they really mean actual_min and
actual_max. On first glance this may seem harmless, but it triggers (in
the netcdf-java library default behavior) a costly scan of the data
looking for invalid data, ie values outside that range.

So adding actual_min/max as recommended attributes should help users
from mistakenly using valid min/max. And its very useful for visualizers
to create color scales etc.

Julia Collins wrote:
> On Mon, 9 Jun 2008, Jon Blower wrote:
>   
>> I have rediscovered this conversation in the depths of my inbox and 
>> thought it might be worth resurrecting.  To summarize the discussion 
>> so far:
>> 1) I proposed two new standard optional CF attributes (called 
>> something like minimum_data_value and maximum_data_value) that would 
>> be attached to a variable in a NetCDF file, redundantly holding its 
>> actual min and max values in that file. [...] As well as helping with

>> data mining applications, this would act as a hint to visualization 
>> packages to provide a first attempt at automatically defining a 
>> colour scale range for sensible portrayal.  Note that this attribute 
>> pair is distinct in purpose from valid_min and valid_max (which 
>> contains theoretical extrema, beyond which data is considered
invalid).
>>     
>
> I support the idea of formalizing these sorts of attributes in some 
> way. However, I would prefer a simpler name(s). For example:
"actual_min"
> and "actual_max." Less typing :-), and more like the existing
"valid_min"
> and "valid_max" attributes.
>
> Julia
> --
> Julia Collins
> National Snow and Ice Data Center
> CIRES, University of Colorado, Boulder
> 449 UCB
> Boulder, CO 80309-0449
> Voice: 303-492-6405
> E-mail: collinsj at nsidc.org
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