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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of John Caron > Sent: 10 June 2008 00:54 > Cc: [email protected] > 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 * ******************************************************* _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
