Dear all,
I think there are at least two types of min/max attributes that one
could associate with a particular variable in a netCDF file:
1) The *actual* min and max of the variable's values in that
particular file (not including missing values). Perhaps stored as
data_min and data_max? Useful for both visualisation and data mining
(as Bryan pointed out).
2) If the netCDF file is part of a larger dataset (e.g. it represents
one timestep in a forecast sequence) it would be useful to store a
"reasonable" (or actual, if possible) min and max for the *whole
dataset* (taking into account the measurement method used,
geographical region etc). Perhaps stored as dataset_min and
dataset_max?
The latter pair of attributes would really help when creating
visualisations of timeseries across multiple netCDF files and could be
a "soft" range: i.e. it could be possible for some data to lie outside
this range (for a forecast dataset it would be impossible to define
the whole dataset's min and max in advance unless it were defined to
be much wider than is really useful for visualisation). I think that
all viz tools should highlight data that are "out of range": it seems
to me to be a serious flaw to do otherwise as it hides potentially
vital data.
If a file specifies neither pair of attributes, perhaps there could be
a community dictionary of suggested ranges per standard name, but this
is flawed for reasons discussed on this thread. Might be better than
nothing though.
Regards, Jon
On 1/4/07, David Stuebe <dstuebe at umassd.edu> wrote:
> Re: attributes for min/max data values for visualization
> (Chris Webster)
>
>
> This is a very important point that Chris has made regarding the need for
> min/max data in visualization. For my work with visualization of FVCOM
> unstructured data, I have only encountered this as an issue while working
> with multi-domain data sets. Since I have multiple files, one for each
> domain plus a master file, I only store min/max data in the master file.
>
> I have found that the min/max data are only useful in this context, where
> certain data may not be useful based on its range and can therefore be
> neglected without reading from disk. My highly >>non<< standard file
> structure for multi-domain data is to break apart a single file into
> seperate files which are identical to the original and complete for
> visualization of that subdomain plus its ghost zones. The master file then
> contains the data reguarding which cells are ghost cells and the min and max
> (spatial and data extents) for each sub-domain. This information can be
> checked first when the user requests a particular plot from the
> visualization program.
>
> Before we get into details like naming schemes for min max values, what are
> the contexts in which this optional min/max data are useful? This will be an
> important determining factor in how it is stored.
>
> David
>
>
>
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>
>
>
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Received on Mon Jan 08 2007 - 03:31:02 GMT
