[galeon] WCS null value intervals?

[Peter Baumann]

Andrea & all-

in an attempt to address currently open items let me come back to the 
issue raised by Andrea Aime / Steven Keens:

Q: should we allow, in WCS 1.2, that null values are identified not only 
by a value or a list of values, but additionally by intervals?

Examples:
    myIntNullValues = { -65534, [-1 ... +1] }
    myFloatNullValues =  { 0, [2.71 ... 3.14], [0.999 ... 1.001] }

Background:
- Currently (WCS 1.1.2) allows zero or more null values in 
wcsDescribeCoverage.xsd:
    0..* ows:CodeType
- in WCS 1.0.0 null values were described by (values.xsd):
    0|1 valueEnumType ("Enumeration of TBD values which consists of a 
sequence of intervals and/or single values.")
I think I remember we gave up at some time when there was no light at 
the end of the complexity tunnel, such as in dealing with open/closed 
boundaries (which are present, but not defined 1.0.0).

Arguments:
pro: was possible in WCS 1.0.0, we shouldn' reduce functionality nor 
backwards compatbility (and 1.0.0 is important for a significant user group)
pro: especially when dealing with floating point numbers it is unstable 
to use specific values and use "==". Intervals allow for a numerically 
appropriate handling.
con: adds complexity to a server implementation, and potentially to a 
client which attempts to seriously deal with null values. (Of course it 
is up to a service to make use of null intervals.)
con: some semantic details seemingly waiting for clarification.

Q to WCS implementors (in particular: GALEON):
1) do you see a need for intervals in your community?
2) would you see null intervals as a severe implementation burden?

thanks,
Peter

-- 
Dr. Peter Baumann
 - Professor of Computer Science, Jacobs University Bremen
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