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[Fwd: Re: NetCDF Toolbox]

Dear Ferreters,

Well, after trying to solve this netCDF file writing dilemma with
the authors of the netCDF package for matlab I thought I'd inquire
with you all.

As I explain below (see forwarded message), I'd like to write a 
netCDf file from matlab so that it is readable AND friendly to ferret.
The problem lies in the multiple grids that I want to use for the single
variable, XC, to be stored in the netCDF file. As I point out, I'd like
XC to be defined over a grid of constant dimension but with the range
of the x-axis to be a function of y. A 'show data' in ferret would
give me:

yes? show data
     currently SET data sets:
    1> /home/server/scratch/oxilia/netcdf/posum_test.cdf  (default)
 name     title          I         J         K         L
 XC                     1:275     1:2       1:1       1:199

My question is: How do I define a VARIABLE grid x(j)? For all j the
dimension of i = [1:275], but the range of the axis in:

yes? shade xc[j=1]

will vary with j. For j=1, the x-axis will have limits [-10,10] say.
For j=2, the limits will be [-7,7].

Anybody know how to make matlab and ferret like eachother? Any
comments would be appreciated.

David.


David Oxilia wrote:
> 
> Chuck,
> 
> Thanks for your reply. I must say that the netCDF format is a bit of
> a mystery to me. Your suggestions were useful but my problem remains.
> I'll try to explain it better. First I should mention that I am not
> clear what the difference is between 'axes variables' and 'axes
> dependent variables'. To my mind, the former specify a 'grid',
> for example, (x,t). The latter are variables which make use of this
> grid. For the above example we'd have say f(x,t).
> 
> The file I want to write consists of ONE single 3D variable, XC(x,y,t)
> which varies 'parametrically' with y. I'll write this as XC(x,t)|y,
> y = 1,...,N. Now, the DIMENSION of my grid (x,t) is constant for all
> y. However, the VALUES assigned to the axis variable x also vary with
> y. Thus, XC(x(y),t)|y is probably a better notation.
> 
> In essence I need to write a different x-axis grid for each y.
> The XC are then written for each y on a different grid even though
> the dimension of the grid doesn't change; only the numerical values
> of x and y.
> 
> I want to be able to read this file into other graphics software
> and make contour plots of XC(x,t). I'd like the plots to have
> labels specifying the y (actually latitude) for each XC(x,t) slice.
> The problem is that the range of values along the x-axis should
> dependent on y. For example, at 5N the x-axis will have a dimension
> of say 100 grid points and its range will be [-10,10]. At 10N
> the x-axis will still have 100 grid points but the range is now
> [-7,7].
> 
> Writing the file as follows:
> 
> % ------------------------------------------------------------
> % Dimensions
> nc('one') = 1;
> nc('latitude') = iymax;
> nc('t') = 2*m-1;
> nc('x') = n;
> 
> % Axes & Variables
> nc{'latitude'} = 'latitude';                    % an axis
> nc{'t'} = 't';                                  % an axis
> nc{'x'} = {'one','one','latitude','x'};         % a 4D axis !!
> nc{'XC'} = {'t','one','latitude','x'};          % a >4D variable?!
> 
> % Attributes
> nc{'latitude'}.units = 'degrees';
> nc{'t'}.units = 'days';
> nc{'x'}.units = 'km';
> nc{'XC'}.units = ' ';
> nc{'XC'}.long_name = 'Time-Longitude Lagged Cross-Correlations';
> 
> % Write data
> nc{'latitude'}(:) = yax;                        % a vector
> nc{'t'}(:) = tlax;                              % a vector
> nc{'x'}(:) = XLAX;                              % a 4D array
> nc{'XC'}(:) = CA;                               % a 4D array
> % ------------------------------------------------------------
> 
> allows me to write the CDF file but the grid used to write XC
> is not 4D since nc{'x'} is a 4D axis! XC believes it has a 7D
> grid rather than a 4D grid.
> 
> Well, I hope this isn't wasting too much of your time. If I
> undertood how grid axes differ from grid variables in CDF maybe
> I could figure out how to do this.
> 
> Thanks again for any suggestions.
> 
> David.

*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
David Oxilia			Tel: (541) 737~2368
COAS:Oregon State University	Fax: (541) 737~2064
Ocean Admin. Bldg. 104		WWW: http://joule.oce.orst.edu/po
Corvallis, OR 97331-5503	Email: oxilia@hejira.oce.orst.edu
*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
--- Begin Message --- 
Chuck,

Thanks for your reply. I must say that the netCDF format is a bit of
a mystery to me. Your suggestions were useful but my problem remains.
I'll try to explain it better. First I should mention that I am not
clear what the difference is between 'axes variables' and 'axes
dependent variables'. To my mind, the former specify a 'grid',
for example, (x,t). The latter are variables which make use of this
grid. For the above example we'd have say f(x,t).

The file I want to write consists of ONE single 3D variable, XC(x,y,t)
which varies 'parametrically' with y. I'll write this as XC(x,t)|y,
y = 1,...,N. Now, the DIMENSION of my grid (x,t) is constant for all
y. However, the VALUES assigned to the axis variable x also vary with
y. Thus, XC(x(y),t)|y is probably a better notation.

In essence I need to write a different x-axis grid for each y.
The XC are then written for each y on a different grid even though
the dimension of the grid doesn't change; only the numerical values
of x and y.

I want to be able to read this file into other graphics software
and make contour plots of XC(x,t). I'd like the plots to have
labels specifying the y (actually latitude) for each XC(x,t) slice.
The problem is that the range of values along the x-axis should
dependent on y. For example, at 5N the x-axis will have a dimension
of say 100 grid points and its range will be [-10,10]. At 10N
the x-axis will still have 100 grid points but the range is now
[-7,7].

Writing the file as follows:

% ------------------------------------------------------------
% Dimensions
nc('one') = 1;
nc('latitude') = iymax;
nc('t') = 2*m-1;
nc('x') = n;

% Axes & Variables
nc{'latitude'} = 'latitude';			% an axis
nc{'t'} = 't';					% an axis
nc{'x'} = {'one','one','latitude','x'};		% a 4D axis !!
nc{'XC'} = {'t','one','latitude','x'};		% a >4D variable?!

% Attributes
nc{'latitude'}.units = 'degrees';
nc{'t'}.units = 'days';
nc{'x'}.units = 'km';
nc{'XC'}.units = ' ';
nc{'XC'}.long_name = 'Time-Longitude Lagged Cross-Correlations';

% Write data
nc{'latitude'}(:) = yax;			% a vector
nc{'t'}(:) = tlax;				% a vector
nc{'x'}(:) = XLAX;				% a 4D array
nc{'XC'}(:) = CA;				% a 4D array
% ------------------------------------------------------------  

allows me to write the CDF file but the grid used to write XC
is not 4D since nc{'x'} is a 4D axis! XC believes it has a 7D
grid rather than a 4D grid.

Well, I hope this isn't wasting too much of your time. If I 
undertood how grid axes differ from grid variables in CDF maybe
I could figure out how to do this.

Thanks again for any suggestions.

David.

*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
David Oxilia                          Tel: (541) 737-2368
COAS-Oregon State University          Fax: (541) 737-2064
Ocean Admin. Bldg. 104
Corvallis, OR 97331-5503              Email: oxilia@hejira.oce.orst.edu
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
--- End Message ---
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