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On 7/25/11 9:51 AM, John Caron wrote:
On 7/21/2011 1:31 PM, Tom Whittaker wrote:The more I think about this, the more I tendtoward the idea that we probably shouldn't try to merge the different kinds of binning into a single all-encompassing coordinate. There is a point atwhich we have to go ahead and split the data into different variables.I agree. We have the issue, for example, of bands that have different units. Since "units" is an attribute of a variable, that would mean that only bands with the same units could be included in the 'array'. This also means that a given file might have more than one "band coordinate variable", since there might be, say, 3 emissive channels and 2 reflective ones with different units.There is nothing preventing you from defining dimensions and coordinate variables for the different binnings of your image data and storing everything into a single variable (with dimensions for wavelength,bandwidth, polarization, applied filter, etc). It is just the question of whether or not some portion of it will be defined via a CF convention, andwhat that portion is.Well stated -- getting at the heart of the matter. I look at this from an application developer's standpoint: when I look at a "data variable" and see that it has dimensions of, say, "abc x y" I would like to know whether "abc" is "time" or "altitude" or...."band" because I'll treat the data differently. And, I may then seek other variables with specific "standard_names" to define things like wavelength, etc. tomI agree that if different bands have different units, these must be in a different variable. That reasoning applies to all of the variable's attributes.Another way to say the same thing: A coordinate variable must have values that are a "sampling" along a continuous domain. One sees this violated in the poorly designed AWIPS netcdf files, eg where all "temperature" values are crammed into one variable, and the coordinate values have both pressure and height and potential temperature, etc.
There are instances where the spectral domain sampling will not be monotonic increasing. For example, AIRS L1B, where 3 broad band regions overlap, but are written into a single array, and MHS, ATMS, where two adjacent bands have the same central frequency, but differ in their respective frequency sampling range. Different applications may have different ideas how they want to interpret this. For example, in the former case we
sort the individual wavenumbers and keep track of the sort indexes.
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