Re: [Pytables-users] NetCDF 4

[Norbert N. <Nor...@gm...>]

Am Dienstag, 25. Januar 2005 18:40 schrieb Francesc Altet:
> A Dilluns 24 Gener 2005 20:51, Norbert Nemec va escriure:
> > In short pseudonotation:
> > I want to store the result of a function
> >  f(x,y,time)
> > as well as another (time independent) function
> >  g(x,y)
> > with
> >  x in range(0.0,2.0,0.1)
> >  y in range(-1.0,1.0,0.1)
> >  time in range(0.0,500.0,10.0)
> >
> > NetCDF allows me to first define the dimensions 'x','y' and 'time' and
> > then write datasets (arrays) that extend in a certain subset of these
> > dimensions.
>
> Uh, can you be a bit more explicit on what feature PyTables is missing?. A
> single metacode would be enough. [You know that EArrays allows extending
> the object in any (single) dimension you want, do you?.]

Never mind. I thought about it a bit more and understand somewhat more now:

NetCDF and HDF have different objectives. The latter is just a kind of a 
container that helps to store and access your data but doesn't associate any 
meaning with it. NetCDF, on the other hand, tries to store data in a 
self-descriptive way. You don't just store a bunch of numbers, but you also 
specify their meaning to a certain extent in a machine readable way.

The example above would mean that you store five arrays:
 x, y, time, f, g
in such a way that it is clear that x,y and time are coordinates, while f and 
g is data at these coordinates.

Of course, this can simply be done on top of HDF5 (which is, what NetCDF4 is 
trying to do - previous versions defined their own file format)

Everybody could find their own convention how to store this kind of 
relationship. The whole point of NetCDF is to fix one convention so that 
various tools can use this additional information to properly handle or 
display the data.

It probably is not the idea behind PyTables to follow this path. Maybe some 
day, one can put something similar to NetCDF on top of PyTables, but it 
should probably always kept as two distinct layers.

Ciao,
Norbert


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