This "breaks" when you subset data via opendap, for example,
doesn't it? I agree that it could be useful for discovery and for
apps like contouring, but it will need to be used carefully.
Although the name would be "actual_min" (or max), the definition
would need to specify that it include only valid data values, otherwise
it won't be useful. Maybe actual_valid_min (or max) would be more
clear, and would save the overhead that the use of valid_min/max
incurs.
Cheers - Nan
> 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.
>>
--
*******************************************************
* Nan Galbraith (508) 289-2444 *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
*******************************************************
Received on Fri Jun 20 2008 - 09:11:14 BST
