Re: [ferret_users] plotting values of 0.0 for variables with scale

Re: [ferret_users] plotting values of 0.0 for variables with scale_factor attribute

To: ferret_users@xxxxxxxx

Subject: Re: [ferret_users] plotting values of 0.0 for variables with scale_factor attribute

From: "Ansley C. Manke" <ansley.b.manke@xxxxxxxx>

Date: Fri, 2 Aug 2019 14:01:38 -0700

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Hi all,

It turns out that this comes from a bug in Ferret/PyFerret in which a variable having scaling and also having only a missing_value attribute but not a _FillValue attribute may show this behavior where 0's are treated as if they're missing. This will be fixed in the next official release.

Ansley

On 8/2/2019 9:58 AM, William Lipscomb wrote:

Hello,

I'm new to this list and to PyFerret (though I've used Ferret for a while). I'm having an issue plotting fields with the netCDF scale_factor attribute. For example, I have a 2D field "thck" (type float) with scale_factor = 1000., and with values of 0.0 in parts of the domain. It seems that ferret gets confused about the zero values.

When I type "list thck", then wherever the value is 0.0, I see four dots instead of the value.

When I type "shade thck", then wherever the value is 0.0, I get a white background instead of the color corresponding to 0.0.

A manual fix is to use NCO to delete the scale_factor attribute and then multiply thck by 1000. The zero values are of course still zero, but now they list and plot correctly.

I was wondering if this is a known issue and if there is a workaround within Ferret, without removing the attribute.

I'm using PyFerret v7.5 (optimized) on a Mac, with Darwin 17.7.0. I have the same problem on Cheyenne, an NCAR HPC using PyFerret 7.5 with Linux 4.12.14-94.41-default. I don't recall having this issue with earlier versions of Ferret (before PyFerret).

Thanks,

Bill

--

William Lipscomb

National Center for Atmospheric Research

Boulder, CO

(505) 699-8016

--
Ansley Manke
NOAA/PMEL Science Data Integration Group
7600 Sand Point Way NE
206-526-6246