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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Firstly, I am having second thoughts about my suggested terms 'external' and 'internal'. A respected colleague thought they meant the opposite of what I meant. So how about just 'disk value' and 'memory value? Or 'physical value' and 'logical value'? > Date: Mon, 23 Apr 2001 13:47:05 -0600 > From: John Caron <caron@xxxxxxxxxxxxxxxx> > Subject: Re: ncdigest V1 #587 (standard handling of scale/offset and missi > ng data) > > > I assume you mean missing_value. There is no problem if missing_value > is > > merely a hint for output. > > You simply alway ignore it (on input at least)! > > I am reading an existing file, theres no option of deleting or forcing > renaming. I want to do as good of job as possible in extracting meaning > out of the file. Someone has taken the time to add a missing_value > attribute to the file. It doesnt seem reasonable to ignore it, because: > if they are followng the UG conventions, it wont be there, so no > problem. The fact that it exists means they arent following the > conventions (or have made a mistake) so you dont know what logic they > are following. In that case, I would fall back on what a reasonalble > person would intend (who doesnt know about the conventions). > If there is no valid range defined, but missing_value is defined, then I can see it makes sense to use a positive value to define a valid max and a non-positive value to define a valid min. (i.e treat it like _FillValue) > I dont understand. If _FillValue can be legal, how can you construct a > valid_range with it, using it as the valid_min or valid_max? It seems > like contradictory uses. > There are two cases. _FillValue is a valid value if it is within a valid range defined by valid_range, valid_min, valid_max. If none of these three attributes are defined then it is assumed that _FillValue is a missing value & should be used to define one end of the valid range. So if you want to use _FillValue to initialize a variable to a valid value 0, then you must define at least one of valid_range, valid_min, valid_max.
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