Hi Joe,
On Oct 25, 2010, at 8:53 AM, J Glassy wrote:
> Herrero,
> I think conceptually what you're referring to needing is to somehow
> represent and insert NULL values into your HDF file, if you really
> don't know the native valid range of the data. A true NULL represents
> something very distinct from any known, valid value, akin to "no
> information is available".
> While routine in most relational database implementations, this
> (may) not be possible using HDF's native facilities.
> The default internal missing value for a HDF5 dataset is 0, but
> you can currently override this exactly once only, at dataset creation
> time, with a user supplied value that fits within the range of the
> datasets datatype (its now a DatasetCreationProperty element).
> Perhaps you can define such a value that is very clearly outside
> the valid range of your sensor, as informed by its hardware design.
> For example, many sensors have built in numerical limits governing
> what they can emit, due to how their A/D conversion works, or to their
> digital hardware/firmware if its is a pure digital sensor (e.g. a 12
> or 14 bit sensor has a very deterministic limit to what it can emit),
> so you could define your "pseudo-null" value as just outside this
> range etc.
> Ideally, the HDF facility proper could someday allow users to
> specify a true NULL value as a missing value, but this can be tricky
> and involve opaque conversions, since internally the value is usually
> represented as some "known,valid" numeric type. HTH
Good suggestions, thanks! I just wanted to add that possibly Vincent
could use the "fill value" facility in HDF5, with H5Pset_fill_value(), although
I suspect that may not fulfill his requirements...
Quincey
> Joe
>
> On Mon, Oct 25, 2010 at 2:34 AM, Herrero Vincent
> <[email protected]> wrote:
>> Hello,
>>
>> I would like to store in a HDF dataset all values sent by a sensor which
>> emits a value at every same period of time (10 ms for example).
>> Sometimes the sensor does not send a value and we would like to see this gap
>> in our HDF dataset.
>>
>> Is it possible to store empty or missing values in a dataset?
>>
>> We do not want to choose a special value for that purpose as we don't know
>> what is the range of acceptable values sent by the sensor.
>>
>> Thanks for your help.
>> Best Regards,
>>
>> Vincent Herrero
>>
>> _______________________________________________
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>>
>>
>
>
>
> --
> ------------------------------------------------------------
> Joseph Glassy
> Lead Software Engineer (contractor)
> NASA Measures (Freeze/Thaw),Rm CFC 424
> College of Forestry and Conservation
> Univ. Montana, Missoula, MT 59812
> Tel: 406-243-6318 Cellular: 406-544-3315
>
> Lupine Logic Inc.
> www.lupinelogic.com
> Scientific and Technical Programming
>
> _______________________________________________
> Hdf-forum is for HDF software users discussion.
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