------- Forwarded Message
>From: HANKIN@xxxxxxxxxxxx
>Date: Mon, 28 Sep 1992 13:42:31 -0800
>Subject: RE: 4D dimensions and other conventions...
>Organization: .
>Keywords: 199209282044.AA08092
>Hello Rich, Tim, Ken, et. al.,
>
>I've been following your discussion about netCDF styles with interest as my ow
> n
>group - a numerical modeling group - shares the similar concerns: how to use
>netCDF to achieve a compatible representations of our model data (gridded,
>multi-gigabyte, multiple variables on staggered grids) as well as PMEL's EPIC
>data (down the hall) and outside institutions, too.
>
>This business of time axis representations is leading us all to similar
>solutions. Rich has described a global variable called "base_date" which
>"specifies the Gregorian start date". Similarly, the file "conventions.info"
>available from unidata.ucar.edu suggests e.g.
>
> variables:
> double time(nobs);
> time:units = "milliseconds since (1992-9-16 10:09:55.3 -600)"
>
>Our own software, FERRET, uses a solution e.g.:
>
> float TIME(TIME) ;
> TIME:units = "seconds" ;
> TIME:time_origin = "14-JAN-1976 14:00:00" ;
>
>and accepts int, long, float, or double data types.
>
>While all of these are very similar solutions they are also incompatible. How
>
>are time-date strings formatted? Where should the time origin be placed: in t
> he
>units string? in a global attribute? in a variable attribute? If in an
>attribute, what is the attribute name? Is the data type mandated? Does the
>axis have to be a "coordinate variable" (dimension name=variable name) ? etc.
>
>etc. Similar issues arise for if/how to map gridded data onto 4-dimensional
>grids. Mandatory ordering of axes? Mandatory axis names? Mandatory units
>choices? What to do with missing axes (e.g. Z axis of vertically averaged
>flow)?
>
>It seems to me that if we want to adopt conventions for these issues now is th
> e
>time to do it. NetCDF can fail to be a "standard" in any meaningful way if
>these issues are not addressed somewhat formally by "users" (us) acting as a
>community. I have some personal experiences with this type of standards-failu
> re
>as a member of the ANSI committee that creates CGM (the Computer Graphics
>Metafile). CGM, a broadly conceived standard, has expected user communities t
> o
>develop "profiles" that dictate their particular style choices and ensure
>interoperability. The user communities have mostly failed to get organized an
> d
>there is chaos in the CGM world - enough to endanger its success as a standard
> .
>
>I spoke to Russ Rew and he agreed that a "straw man" proposal on these
>conventions for oceanographers was in order. I will try to pull one together
> in
>the next few days - using "conventions.info" as a starting point but going int
> o
>much greater detail. My main goal will be to enumerate the open issues. The
>list I generate will be VERY incomplete - I hope we can pass it around and add
>
>to it. When we have a moderately exhaustive list then we can begin discussing
>
>solutions that encompass our issues.
>
>If you see a problem with this process please fire away!
>
> cheers - steve
>
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