[ferret_users] Reading NetcDF attributes with higher precision with ferret

[Jacques Stum <jacques.stum@xxxxxx>]

Hello Ferret users,

I have a precision problem to plot a particular value of my variable 
"chlorophyll_concentration" with ferret :
I read this variable from a NetCDF file, which contains a lat-lon grid 
of 84*log(chlorophyll_concentration) stored on a byte.

This is the result of "show data" :

name     title                                        I              
J         K         L
CHLOROPHYLL_CONCENTRATION
         log(chlorophyll-a in mg/m3)      1:2627    1:2100    ...       ...


I have set _FillValue=127 in the NetCDF file
I have also set two additional "out of range" values  :126 to describe a 
land mask, and 125 to describe the cloud mask
A scale factor = 1/84 is set in the NetCDF file, so ferret displays the 
log of chlorophyll.

! reading the scale factor
LET sc = chlorophyll_concentration.scale_factor
list sc outputs at the screen 0.0190 (instead of 0.011904762 which is 
the more exact value of 1/84)

shade/levels=(`sc*126`,`sc*126`,1)/title="land mask" 
"chlorophyll_concentration" gives a correct result : (maybe because 
sc*126 = 1.50000000)
The land mask value appear in pink, with only one pink colour on the 
palette, with lower boundary = 1.5 and upper boundary = 1.5

shade/levels=(`sc*125`,`sc*125`,1)/title="cloud mask" 
"chlorophyll_concentration" does not work (no cloud values displayed), 
maybe because sc*125 = 1.4888095238 ?
The palette on the right is with only one pink colour on the palette, 
with lower boundary = 1.49 and upper boundary = 1.49


Of course, I have checked that values = 125 are present in my variable !

Is there a way to improve the precision of the scale factor read with 
ferret, or doing with other means ?

Thank you for your help

Jacques



--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
JACQUES STUM                                  	     ~~	  E-mail	 :  jstum@xxxxxx	
Collecte Localisation Satellite,
8-10 rue Hermès,                                 	     ~~	  Phone   :  33 5 61 39 48 12
Parc Technologique du Canal,
31526 Ramonville Saint-Agne, France	     ~~    	  Fax	 :  33 5 61 39 37 82
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