Thanks Jonathan.
Here's a brief description of my use case. I have a collection of
NetCDF files (ocean forecast and analysis) and I have written a Web
Map Service that largely configures itself, based on the contents of
the (CF) metadata in the files. I want to avoid, as far as possible,
manual configuration of the server.
Most variables (i.e. WMS layers) are scalar quantities, but I'd like
my software to be able to automatically detect those layers that
represent the components of a vector quantity. Then I can present,
through the WMS, a new "virtual" layer that is rendered by default as
vectors (arrows).
As a particular example, many of the NetCDF files in question have
component variables called "northward_sea_water_velocity" and
"eastward_sea_water_velocity". I'd like to present these through the
WMS as a single layer called "sea_water_velocity" that is rendered as
a vector field.
There are also examples that use magnitude and direction, e.g.
"wind_from_direction" and "wind_speed".
No doubt there will also be examples that give the components of the
velocity along the grid unit vectors rather than "northward" and
"eastward".
I have only considered horizontal 2-D fields (for display on maps) but
no doubt there will be cases where software will need to detect and
display 3-D vector fields.
Jon
On 4/27/07, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
> Dear Jon
>
> There is no way to do this at present in CF, but this is not the first time
> the question has been asked. It could be done by introducing new standard
> names which did not specify the component, and having a dimension running over
> components, with values such as eastward, northward, x and y. I expect other
> approaches are possible.
>
> It would be helpful if you could describe a particular use-case.
>
> Best wishes
>
> Jonathan
>
>
>
> > As you know, vector quanties such as velocities are often represented
> > in CF-NetCDF as two separate component fields (e.g.
> > "northward_sea_water_velocity" and "eastward_sea_water_velocity"). Is
> > there a standard way in CF to represent vector quantities? E.g. in
> > the above case could the two component fields be combined to give a
> > single two-component variable called "horizontal_sea_water_velocity"
> > or whatever the best standard name is? Is there any way to
> > unambiguously represent the fact that two or more fields in a NetCDF
> > file represent the components of a vector quantity (other than by
> > interpreting the standard name)?
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>
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Received on Fri Apr 27 2007 - 10:37:59 BST
