Re: clarification on MC descriptor files

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi,
    From user manual Ch2 Sec2.1. Multi-file NetCDF data sets

	3)    (note) Previous to version 5.2, each file is
self-documenting with respect to the time axis of the variables -even if
the time axis represents only a single point. (All of the time axes must
be identically encoded with respect to units and date of the time
origin.)   "In version 5.3 and higher these checks are not performed. This
means that the MC descriptor mechanism can be used to associate into time
series groups of files that are not internally self-documenting with
respect to time". 

      Now regarding your problem: 
	you have 
		hourly data ==>      D_TIME_UNIT = 3600  (in seconds)
	 	with different T0 ==> never mind ( provided your ferret
 			    version is higher than 5.3 & data time
                            points are continuous..ie. 61 files means 
	                    hourly data from some hr in day 1 to some hour 
                            in day 61 without missing any hour in between)
                solution ==> take one T0 ( say T0 of the 1st days file),
                                 give S_START & S_END for each 
			         file according to this T0

                    suppose D_T0TIME      = '30-JUL-1993 01:00:00'  
                            D_TIME_UNIT   = 3600.0,

                    suppose your 1st time point in first file  is 
					"30-jul-1993:01:00:00" ...then

                    for 1st file    S_START  = 0  &  S_END = 23  
                    for 2nd file    S_START  = 24 &  S_END = 47
                    for 3rd fiel    S_START  = 48 &  S_END = 71 & so on

  Hope now you will be able to trace your earlier problem with "error in
line definition A gap or overlap exists in time axis" 
		==> you have same S_START & S_END values for first and 
			and second file, as you can see it is not 
			"continuous in time"         

 A corrected form of your descriptor file is given below. Remember there 
is a limit in the maximum number of files you can include in a descriptor
file (... 400 or 500 i think). Don't forget to cross check the
data accessed through the descriptor file with the original data, in all
aspects (including time).

 
With Regards 

Jaison
 
======================corrected descriptor file====================

  &FORMAT_RECORD
   D_TYPE        =  '  MC',
   D_FORMAT      =  '  1A',
  /
  &BACKGROUND_RECORD
   D_TITLE       =  'Control',
   D_T0TIME      = '30-JUL-1993 01:00:00',
   D_TIME_UNIT   = 3600.0,
   D_TIME_MODULO = .FALSE.,
  /
  &MESSAGE_RECORD
   D_MESSAGE     =  '    ',
   D_ALERT_ON_OPEN      = F,
   D_ALERT_ON_OUTPUT    = F,
   /
   &EXTRA_RECORD
   /
   &STEPFILE_RECORD
    S_FILENAME = '/rcm/dissertation/coarse_control/MMOUT_DOMAIN1_60.nc'
   S_START  =    0,
   S_END    =  23,
   S_DELTA  = 1,
   S_NUM_OF_FILES  =   1,
  /
   &STEPFILE_RECORD
   /
    S_FILENAME ='/rcm/dissertation/coarse_control/MMOUT_DOMAIN1_61.nc'
    S_START  =    24,
    S_END    =  47,
    S_DELTA  = 60,
    S_NUM_OF_FILES  =   1,
   /
   &STEPFILE_RECORD
    s_filename    = '**END OF STEPFILES**'
   /
=============================================================
 

On Wed, 25 Feb 2004, Chris Anderson wrote:

> 
> Hi,
> 
> I have another question regarding MC files.  First, thanks to those who 
> responded to my first question.  Your suggestions have helped me get up to 
> speed very quickly.
> 
> My situation is this.  I have 61 netcdf files.  Each file contains 24 
> hours of model output at an hourly interval.  The time coordinate is the 
> tricky part.  The time coordinate uses a relative time axis.  The 
> reference time is unique to each file.  For example:
> MMOUT_DOMAIN1_01.nc has reference time of 1-JUN-1993 01:00:00
> MMOUT_DOMAIN1_02.nc has reference time of 2-JUN-1993 01:00:00
> ...
> MMOUT_DOMAIN1_61.nc has reference time of 31-JUL-1993 01:00:00
> 
> If I understand the namelist file format, there can be only one reference 
> time as specified by setting D_T0TIME.  If this is true, then the only 
> option I see to use the MC capability is to rewrite the netcdf files with 
> a fixed reference time.  Does this seem correct?  Does anyone know of an 
> alternative?  (I have a lot of netcdf files, actually much more than 
> 61, and I'm hoping for a more convenient approach than rewriting all of my 
> files.)
> 
> BTW, this is the error message I received when I asked ferret to use the 
> example.des file shown below.
> 
> yes? set data example.des
>  **TMAP ERR: error in line definition
>              A gap or overlap exists in time axis
> 
> 
> 
> 
> example.des
>  &FORMAT_RECORD
>   D_TYPE        =  '  MC',
>   D_FORMAT      =  '  1A',
>  /
>  &BACKGROUND_RECORD
>   D_TITLE       =  'Control',
>   D_T0TIME      = '30-JUL-1993 01:00:00',
>   D_TIME_UNIT   = 60.0,
>   D_TIME_MODULO = .FALSE.,
>  /
>  &MESSAGE_RECORD
>   D_MESSAGE     =  '    ',
>   D_ALERT_ON_OPEN      = F,
>   D_ALERT_ON_OUTPUT    = F,
>  /
>  &EXTRA_RECORD
>  /
>  &STEPFILE_RECORD
>   S_FILENAME      ='/rcm/dissertation/coarse_control/MMOUT_DOMAIN1_60.nc'
>   S_START  =    0,
>   S_END    =  1380,
>   S_DELTA  = 60,
>   S_NUM_OF_FILES  =   1,
>  /
>  &STEPFILE_RECORD
>  /
>  &STEPFILE_RECORD
>   S_FILENAME      ='/rcm/dissertation/coarse_control/MMOUT_DOMAIN1_61.nc'
>   S_START  =    0,
>   S_END    =  1380,
>   S_DELTA  = 60,
>   S_NUM_OF_FILES  =   1,
>  /
>  &STEPFILE_RECORD
>   s_filename    = '**END OF STEPFILES**'
>  /
>