On 9/19/2013 3:58 PM, Schultz, Martin wrote:
Now, here is another use case, which we haven't implemented yet - partly
because we didn't see how it can be done in a CF consistent way:
While there has been a definition of a standard file layout for data from multiple
stations (a contribution from Ben Domenico and Stefano Nativi if I am not mistaken), this
concept cannot be applied to multiple aircraft flight data. The station data can be
packaged together with help of a non-geophysical "station" coordinate, because
all stations share the same time axis. With aircraft flights, the time axes often don't
overlap, and forcing all data onto the superset of time would be a tremendous waste of
space. Groups would seem as the natural solution to this problem! Why not flat files?
Because you might wish to retrieve all the aircraft data which were sampled in a given
region during a specific period (a natural use case for a catalogue query it seems) in
one entity, and not in N entities, where you cannot even predict N.
Hi Martin:
if i understand this example, you could use any of the DSG trajectory
forms to have seperate time coordinates for each aircraft track, eg for
multidimensional representation (4.1) :
double time(trajectory, obs) ;
this one assumes you have (about) the same number of observation for
each flight. The ragged array representation (4.3 and 4.4) would allow
you to efficiently store any number of obs for each flight, and each obs
would have its own time coordinate.
The DSG was indeed intended to enable spatial/temporal queries over the
dataset. A natural organization might be to "time partition" the data
(all flights for a day in one file). One either searches through the
files for spatial subsets or employs an external spatial index. The TDS
will do spatial/temporal subsetting on time partitioned DSG files,
though we dont yet have a spatial index.
John
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