[gradsusr] [EXTERNAL] Re: Time: confused between grid vs. world coordinates

Adams, Jennifer M. (GSFC-610.2)[ADNET SYSTEMS INC] jennifer.m.adams at nasa.gov
Tue Jul 16 12:40:45 EDT 2019

I think Ferret is unfazed by non-linear time axes. Perhaps Matlab and IDL as well, because they can handle the 2D lon/lat data for non-rectilinear grids. I am not sure about the netcdf handler for Python. I don't know too much about other tools because I prefer to use GrADS for plotting and data manipulation. 

Jennifer Miletta Adams
ADNET Systems, Inc.
NASA/GSFC, Code 610.2
Building 32, Room S159
(301) 614-6070

On 7/16/19, 8:18 AM, "gradsusr on behalf of gilles delaygue" <gradsusr-bounces at gradsusr.org on behalf of gilles.delaygue at univ-grenoble-alpes.fr> wrote:

    Thanks again for your explanations.
    This is a bit off topic, but which ‘other tools which deal with time axis metadata’ do you know?
    All the best, gilles
    > On 16 Jul 2019, at 13:06, Jennifer M Adams <jadams21 at gmu.edu> wrote:
    > The requirement of a linear time axis is a strong contributor to the fast performace of GrADS. If this constraint is incompatible with your needs, there are other tools that will take the time to read all the time axis metadata and deal with it accordingly. 
    > The documentation for TDEF (https://urldefense.proofpoint.com/v2/url?u=http-3A__cola.gmu.edu_grads_gadoc_descriptorfile.html-23TDEF&d=DwIGaQ&c=ApwzowJNAKKw3xye91w7BE1XMRKi2LN9kiMk5Csz9Zk&r=M2mFZsxo0ZoztoK2Lyoypu1kKkBVKyEoM9CXGWO42zk&m=tHb-R5CRfbdNX5js0GhKfSfFv6sMkXrLKJrSEHC-TXE&s=mBSJD43zHF7pSfIGNWLsCYH7Uch1xOdg11VaXj2FtHI&e= ) says, "The method by which times are assigned to T grid points is always LINEAR.”
    > —Jennifer
    >> On Jul 16, 2019, at 1:45 AM, gilles delaygue <gilles.delaygue at univ-grenoble-alpes.fr> wrote:
    >> Thanks for your answer, and solution. Do you know whether this (strong) limitation of GrADS on the time axis is documented anywhere?
    >> With my best regards, gilles
    >>> On 11 Jul 2019, at 14:01, Adams, Jennifer M. (GSFC-610.2)[ADNET SYSTEMS INC] <jennifer.m.adams at nasa.gov> wrote:
    >>> Yes, GrADS requires a linear time axis with a constant interval between time steps. The only workaround I can think of is to break up your file into pieces, one time step per file, with a naming convention that contains sufficient information about the date associated with your file so that you can use templating. Then create a descriptor file with the daily time axis increment and enough time steps to cover the entire period to span your data, and then GrADS will populate the time steps where your data files exist and treat the rest as missing data. 
    >>> --Jennifer
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