Tom Whittaker wrote:
> On Tue, Jun 22, 2010 at 1:42 PM, Tom Rink <rink@xxxxxxxxxxxxx> wrote:
> >
> > For single band files, will it be necessary to dimension the data array
> > like Data(band, y, x) =A0where band is length=3D1, or is there some other
> > metadata construct which would allow a band=3D1 dimension in the
> > file, but allow Data(y,x), with other band indexed variables like
> > wavelength(band)?
>
> My option: since the application will have to recognize the other
> metadata in order to ascertain that this file has "image data", then
> it probably could be smart enough to realize that if the "band"
> dimension is not part of the shape of the data, that it can (and
> should) default to "1".
The CF Conventions provide for this, with the concept of s "scalar
coordinate variable", defined as:
A scalar variable that contains coordinate data. Functionally
equivalent to either a size one coordinate variable or a size one
auxiliary coordinate variable.
In section 2.4, this is further explained:
Dimensions may be of any size, including unity. When a single value
of some coordinate applies to all the values in a variable, the
recommended means of attaching this information to the variable is
by use of a dimension of size unity with a one-element coordinate
variable. It is also acceptable to use a scalar coordinate variable
which eliminates the need for an associated size one dimension in
the data variable. The advantage of using a coordinate variable is
that all its attributes can be used to describe the single-valued
quantity, including boundaries. For example, a variable containing
data for temperature at 1.5 m above the ground has a single-valued
coordinate supplying a height of 1.5 m, and a time-mean quantity has
a single-valued time coordinate with an associated boundary variable
to record the start and end of the averaging period.
So you could have Data(y,x), a scalar "band" variable, and connnect it
with the Data variable through the CF "coordinates" attribute, declare
the bounds of the band, etc.
float Data (y, x);
Data:coordinates = "band y x";
double band;
band:bounds = "band_bounds";
double band_bounds(2);
band_bounds:units = ...;
--Russ
