[ferret_users] Bug with add_offset/scale_factor and descriptor files

[<Peter.J.Turner@xxxxxxxx>]

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