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Re: [ferret_users] RE: Error in plotting time series data with 6.1?



Hi Mike,
I believe point-spacing is an attribute in the CF standard. And yes, it should be point_spacing = "even"  or "uneven". 

McCann, Mike wrote:
Hi Ansley,
 
Thanks for the quick response.  Just to be clear, the correct point_spacing attributes values should be "even" or "uneven", correct? 
I don't recall seeing point_spacing as an axis attribute in CF Metadata conventions (their servers are down until Friday :-( ).  Seems like a useful attribute that perhaps should be added to the convention.
 
I would like to change my time axis origin, but unfortunately not all the software we use is as smart as Ferret.  We're pretty tightly wedded to Unix epoch seconds for our time axes.
 
-Mike


From: Ansley Manke [mailto:Ansley.B.Manke@xxxxxxxx]
Sent: Wednesday, August 27, 2008 9:40 AM
To: McCann, Mike
Cc: oar.pmel.ferret_users@xxxxxxxx
Subject: Re: [ferret_users] RE: Error in plotting time series data with 6.1?

Hi Mike,
There is a bug in the code that detects whether an axis is irregular!  I also ran into this, just this week.  We'll get it fixed in the next release. Unfortunately the code does a check for "is it actually regular" whether or not you have a point-spacing = regular attribute. I will change that also, so that if the file says it's irregular it will be treated as irregular no matter what.

What would help as a workaround is to make the time origin closer to the start of the data, say t0=1-jan-2000 if that's possible.  The code is looking at the size of delta-t relative to the time coordinates themselves. Comparing the size of delta-t of  seconds out of 1162774813 total seconds since the start of 1970 is more difficult than comparing the size of delta-t relative to a smaller number of seconds since year 2000.  Again, we'll fix it so this WILL work, in the next version.

Ansley



McCann, Mike wrote:
Hi again,
 
I generated another netCDF file with fewer points (10-minute interval sampling from the original data) and Ferret properly recognizes the time axis as irregular:
> ferret
        NOAA/PMEL TMAP
        FERRET v6.1
        Linux(g77) 2.4.21-32 - 03/25/08
        26-Aug-08 13:11
yes? use "http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/mse2006/200609/mse2006_ctd_20061106_original.nc"
yes? show grid GAF1
    GRID GAF1
 name       axis              # pts   start                end
 LONGITUDE LONGITUDE            1mr   122.89W(-122.89)     122.89W(-122.89)
 LATITUDE  LATITUDE             1 r   36.237N              36.237N
 NOMINALDEPTH DEPTH (m)         1 r-  3450                 3450
 ESECS     TIME             14760 i   06-NOV-2006 01:00    27-APR-2007 23:50
Ferret thinks that the 2-minute interval data is regular:
yes? use "http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/mse2006/200609/mse2006_ctd_20061106_original_120.nc"
yes? show grid GMH1
    GRID GMH1
 name       axis              # pts   start                end
 LONGITUDE LONGITUDE            1mr   122.89W(-122.89)     122.89W(-122.89)
 LATITUDE  LATITUDE             1 r   36.237N              36.237N
 NOMINALDEPTH DEPTH (m)         1 r-  3450                 3450
 ESECS1    TIME             68919 r   06-NOV-2006 01:00    27-APR-2007 23:48

      
Seems like Ferret is making a decision to make the time axis regular even though it's not.  Should I provide some help by adding an attribute of 'point_spacing: "uneven"' to the time axis definition in the netCDF file?
 
-Mike
 


From: McCann, Mike
Sent: Tuesday, August 26, 2008 10:32 AM
To: ferret_users@xxxxxxxx
Subject: Error in plotting time series data with 6.1?

Hello,
 
We just upgraded to Ferret 6.1 on a Linux host and I'm getting strange results in plotting an irregular time series. 
 
Here's the plot with an older version running on my Windows box (plots correctly):
bash-2.05$ ferret
        NOAA/PMEL TMAP
        FERRET v5.51
        cygwin 1.3.x - 02/28/03
        26-Aug-08 10:06
yes? use "http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/mse2006/200609/mse2006_ctd_20061106_original_120.nc"
yes? plot PRESSURE
 
Here's the plot with the current release running on my RH Linux (seems to treat the time series as regular) :
> ferret
        NOAA/PMEL TMAP
        FERRET v6.1
        Linux(g77) 2.4.21-32 - 03/25/08
        26-Aug-08 10:07
yes? use "http://dods.mbari.org/cgi-bin/nph-nc/data/ssdsdata/deployments/mse2006/200609/mse2006_ctd_20061106_original_120.nc"
yes? plot PRESSURE
    
 
Any help or suggestions are appreciated.
 
-Mike
 
--
Mike McCann
Software Engineer
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039-9644
Voice: 831.775.1769  Fax: 831.775.1736 http://www.mbari.org


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