Re: [ferret_users] Bug with add_offset/scale_factor and descriptorfiles

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Peter,
Could you send ne the example descriptor file and one or two stepfiles 
that illustrate this?  There weren't any changes in Ferret v5.81 that 
changed how it works with scale factors or descriptor files, but version 
5.80 had a change that might relate to the problem. Previously the scale 
factor and offset found in the first stepfile were applied to all 
stepfiles in a multi-file set.  With v5.80 we had Ferret read the scale 
factors from each stepfile and apply them to the data in that stepfile.

http://www.ferret.noaa.gov/Ferret/Documentation/Release_Notes/v58.html#vary_scale_mc

Ansley

Peter.J.Turner@csiro.au wrote:

> Hello,
>        I have been using LAS to place SST data online. The system was
> working OK until a couple of months ago when we upgraded Ferret and LAS.
> The data we are serving is in netcdf files stored as 8 bit (xyt) with
> add_offset and a scale_factor and the files are linked using a
> descriptor file. It took a little while to notice, but after the upgrade
> the data retrieved were no longer being scaled using the scale_factor
> and add_offset.  I then upgraded to Ferret 5.81 and the latest version
> of LAS but the problem persisted.
>
> I have now narrowed the problem down to Ferret.  I created a new
> descriptor file just pointing at one data file and was able to show that
> if I opened the netcdf file directly (set data "sstnok.nc") selected a
> region and did a shade plot the scale was correctly applied, but if I
> used a descriptor file (set data tnok) (ntok.des) and did the set region
> and shade plot the data was no longer scaled. 
> On further investigation I have found that if I reduce the number of
> variables and attributes in the netcdf file before the variable
> (rewriting the netcdf file in a different order) I am trying to plot
> then the data will scale correctly when initialized through the
> descriptor file. 
> I do not think I can quantify the symptoms much better, has anyone else
> had this rather obscure problem?  I am not a big Ferret user and could
> be doing something stupid and would appreciate some assistance in
> resolving the problem. I can provide some example code etc which should
> show the problem if anyone is interested! 
> Regards
>
> Peter
>
> (PS running under Linux 2.6.8-24-smp)
>
> CSIRO Marine and Atmospheric Research
> Australia
>
>