Re: [CF-metadata] Overlapping vertical bounds

Ansley C. Manke Mon, 06 Mar 2017 10:20:23 -0800

Hi Evan,

Another couple of comments on using a file with overlapping bounds inFerret. Ferret does not have any grid operations that handle suchbounds, but you can make use of the bounds as a variable in your Ferretsession. The full message:


   yes? use file.nc
   *** NOTE: Axis definition error on axis: ZAX. Bounds describe cells
   that overlap one another
     *** NOTE: Error in bounds "ZAX_bnds" or bounds do not enclose
   point on axis ZAX
     *** NOTE: Substituting coordinate midpoints

   yes? list/k=1:5 z[gz=var]
   yes? list/k=1:5 ZAX_bnds

The bounds are available in this 2-by-K variable, and you could make useof it in expressions that you define.


-Ansley

On 3/3/2017 3:59 PM, Ansley C. Manke wrote:

Hi Evan,
The data model in Ferret does not allow for overlapping bounds, nordoes it allow non-contiguous bounds. Those are legal in CF, butFerret (as I imagine is the case for most software), does notimplement everything in the standard.
In fact Ferret will not make use of your bounds definition; I believeit will have ignored the bounds and will instead have defined thegrid-cell edges using the midpoints between axes. Use the command,
   show axis/z axis_name
to see what Ferret has done to set up its the internal representationof the axis.
-Ansley


On 3/3/2017 7:32 AM, Manning, Evan M (398B) wrote:
When I was researching  the topic I came across this:
>/When I try and load the file using Ferret, this throws a warning..Which/
>/makes me think I¹m not doing things correctly:/

>//

>/Ferret v6.93/

>/yes? use file.nc/
>/ *** NOTE: Axis definition error on axis: time. Bounds describecells that/
>/overlap one another/
which made me think that overlap was an error. But reading morecontext I see it is just a “note”, not an “error”, and clearlyoverlapping bounds are accepted.
For my situation of overlapping vertical trapezoids, I now think Ishould use the full overlapping extent in the “bounds” variable andexplain the full shape of the trapezoids in the main variable’sdescription attribute.
Is there a better way to communicate the full situation?

  -- Evan

*From: *Jim Biard <[email protected]>
*Date: *Friday, March 3, 2017 at 5:09 AM
*To: *<[email protected]>
*Subject: *Re: [CF-metadata] Overlapping vertical bounds

What makes you think overlapping bounds are illegal?

On 3/2/17 7:20 PM, Manning, Evan M (398B) wrote:

    I have some quantities which are defined on trapezoids in the
    vertical direction.

    For example the top trap might be full weight from the top of the
    atmosphere (TOA) to 50 hPa, then we ramp linearly between the
    first and second traps between 50 & 75 hPa, then trap 2 is full
    weight 75-100 hPa, followed by another transition in [100, 125]
    hPa, etc.

    I can’t have a bounds variable with the full extent of each trap
    like [ [0, 75], [50, 125], [100, … because overlap is illegal.

    I could have underlap, just giving the intervals where each trap
    is in full force: [ [0, 50], [75, 100], …

    Or I could use the midpoints of the transitions: [ [ 0, 62.5],
    [62.5, 112.5], …

    I’d prefer to find a standard way to communicate the precise
    situation.  Is there one?

      -- Evan




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Re: [CF-metadata] Overlapping vertical bounds

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