have you looked closely into reduced grids and compressed grids?
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/cf-conventions.html#reduced-horizontal-grid
http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/cf-conventions.html#compression-by-gathering
On Wed, Apr 11, 2012 at 2:23 PM, Randy Horne <rhorne at excaliburlabs.com> wrote:
> Jim:
>
> In our use case, software is simplified, not because of the removal of a
> multiply and an addition, but as a result of the coordinate variable values
> always having values starting at 0, and ascending monotonically and
> sequentially (i.e. 0, 1, 2, 3 ?n), and just pulling specific add_offsets and
> scale_factors out of a table where the table has an entry for each type of
> product.
>
> vey respectfully,
>
> randy
>
>
> On Apr 11, 2012, at 1:05 PM, Jim Biard wrote:
>
> Hi.
>
> I'm not against expanding the use of scale and offset, per se, but the
> reasons that you would like to use them seem (to me) to not be generally
> applicable. ?Argument 1) implies that you obtain some sort of measurable
> benefit from saving one multiplication and one addition in your production
> software. ?If you have optimized your code so well that this represents a
> major improvement, you are to be congratulated, but that won't be true for
> most. ?Argument 2) does not appear to be something you can count on in every
> circumstance, nor do I think it advisable to imbue the scale_factor
> attribute with any such interpretation as a general rule.
>
> I am finding it often the case for swath data that coordinate variables end
> up occupying a larger portion of a file than data variables. ?I think it's a
> great idea to address this issue. ?I must admit I'm not sure what the best
> way is.
>
> Grace and peace,
>
> Jim
>
> Jim Biard
> Research Scholar
> Cooperative Institute for Climate and Satellites
> Remote Sensing and Applications Division
> National Climatic Data Center
> 151 Patton Ave, Asheville, NC 28801-5001
>
> jim.biard at noaa.gov
> 828-271-4900
>
> On Apr 11, 2012, at 10:50 AM, Randy Horne wrote:
>
>
> The allure of using add_offset & scale_factor with coordinate variables goes
> beyond saving space. ??For example, in our use case ?
>
> (1)
> Makes the s/w producing the product simpler.
>
> (2)
> The scale_factor also tells you what the horizontal spatial resolution is in
> a representation that aligns with the coordinate space.
>
>
> very respectfully,
>
> randy
>
>
>
> On Apr 10, 2012, at 3:11 PM, Etienne Tourigny wrote:
>
> If netcdf-4 is an option for you, it might be simpler to compress
>
> (deflate) the coordinate variables, this works transparently.
>
>
> Etienne
>
>
> On Tue, Apr 10, 2012 at 2:40 PM, David Hassell
>
> <d.c.hassell at reading.ac.uk> wrote:
>
> Hello Randy,
>
>
> I, too, recently thought about this when working on some CF processing
>
> software (cf-python), but couldn't think of a use case so didn't
>
> pursue it - and now you have one!
>
>
> It seems to me that the use of scale_factor and add_offset is intended
>
> for (but not restricted to ...?) the reduction of dataset size
>
> (chapter 8). Is the requirement in your example for space saving, or
>
> some other convienience? I personally think that the latter case is
>
> better served by an appropiate setting of the units attribute (such as
>
> units="0.555555555555556 K _at_ 459.67" if we have converted from Kelvin
>
> to Fahrenheit).
>
>
> Anyway, I can't think of a reason not to allow these attributes on
>
> coordinates - these variables can be very large, after all.
>
>
> All the best,
>
>
> David
>
>
> ---- Original message from Randy Horne (01PM 05 Apr 12)
>
>
> Date: Thu, 5 Apr 2012 13:05:45 -0400
>
> From: Randy Horne <rhorne at excaliburlabs.com>
>
> To: cf-metadata at cgd.ucar.edu
>
> X-Mailer: <IMail v8.21>
>
> Subject: [CF-metadata] Using add_offset & scale_factor with coordinate
>
> variables
>
>
> Folks:
>
>
> Appendix A, Table A.1 in the CF conventions state that add_offset and
> scale_factor can be used with data variables, but not coordinate variables.
>
>
> For the data producing system I am working (GOES-R Ground Segment) it is
> particularly convenient to make use of add_offset and scale_factor with our
> coordinate variables.
>
>
> Is there an issue with changing the conventions to allow this ?
>
>
> very respectfully,
>
>
> randy
>
>
>
>
>
> ..............End of Message ...............................-->
>
>
>
>
>
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>
>
> --
>
> David Hassell
>
> National Centre for Atmospheric Science (NCAS)
>
> Department of Meteorology, University of Reading,
>
> Earley Gate, PO Box 243,
>
> Reading RG6 6BB, U.K.
>
>
> Tel ??: 0118 3785613
>
> Fax ??: 0118 3788316
>
> E-mail: d.c.hassell at reading.ac.uk
>
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> ____________________________________
>
> Randy C. Horne (rhorne at excaliburlabs.com)
> Principal Engineer, Excalibur Laboratories Inc.
> voice & fax: (321) 952.5100
> url: http://www.excaliburlabs.com
>
>
>
>
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> ____________________________________
>
> Randy C. Horne (rhorne at excaliburlabs.com)
> Principal Engineer, Excalibur Laboratories Inc.
> voice & fax: (321) 952.5100
> url: http://www.excaliburlabs.com
>
>
>
>
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Received on Wed Apr 11 2012 - 12:11:23 BST
