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Known time desc » History » Version 29

Anonymous, 08/07/2016 12:15 PM

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h1. Known time description
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h2. Double Time ranges : date from 01/01/1970 to 01/01/2100
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* seconds from 01/01/1970 00:00:00  :                                                 0          to            4 102 488 000
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* milliseconds from 01/01/1970 00:00:00  :                                          0          to    4 102 488 000 000    (ambiguity for the first 48days of 1970 with previous time format)
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* seconds from 01/01/0000 00:00:00  :                       62 168 472 000          to          66 270 960 000 (no ambiguity)
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* milliseconds from 01/01/0000 00:00:00 :        62 168 472 000 000           to 66 270 960 000 000 (no ambiguity)
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* seconds from 01/01/2000 00:00:00  :                          - 946 728 000          to            3 155 760 000  (TT2000)
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* milliseconds from 01/01/2000 00:00:00  :           - 946 728 000 000          to    3 155 760 000 000 (ambiguity with TT2000 in seconds?)
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µs, ns, ps might also be needed for tt2000
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Double (IEEE754) 	
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64bits  	
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min value: -1.7977E+308 	
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max value :1.7977E+308
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h2. Known time description
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|_.Mission Name |_.time var name                   |_. units         |_.DEPEND |_.LABLAXIS|_.FIELDNAM                   |_.CATDESC                                                         |_.Type                         |_.VIRTUAL|_.nb of records|_.VAR_NOTES|
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|Cluster FGM        |time_tags__CDFNAME     |ms                 |0                   |UT                 |Universal Time               |Interval centred time tag                                    |CDF_EPOCH            |                     |normal              |field missing|
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|Cluster HIA          |time_tags__CDFNAME     |ms                 |0                   |UT                 |Center Time                    |Interval centred time tag                                    |CDF_EPOCH            |                     |normal              |field missing|
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|Themis Efi,SCM  |VARNAME_time                 |sec                |TIME            |UT                 |Same as time var name|UTC, in seconds sinc 01-Jan-1970 00:00:00|CDF_DOUBLE          |                     |normal              |Unleaped seconds|
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|Themis Efi,SCM  |VARNAME_epoch             |field missing|0                   |UT                 |Same as time var name|Unrelated                                                              |CDF_EPOCH           |true              |0                        |field missing|
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|Themis Efi,SCM  |VARNAME_dot0_epoch0|msec             |EPOCH0    |UT                 |Same as time var name|EPOCH of THEMIS time base                           |CDF_EPOCH            |                     |1                        |EPOCH of 01-Jan-1970 00:00:00|
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|Themis Esa          |VARNAME_time                 |sec                |TIME            |UT                 |Same as time var name|UTC, in seconds sinc 01-Jan-1970 00:00:00|CDF_REAL8             |                     |normal              |Unleaped seconds|
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|Themis Esa          |VARNAME_epoch             |field missing|0                   |UT                 |Same as time var name|Unrelated                                                              |CDF_EPOCH           |true              |0                        |field missing|
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|Themis Esa          |VARNAME_dot0_epoch0|msec             |EPOCH0    |UT                 |Same as time var name|EPOCH of THEMIS time base                           |CDF_EPOCH            |                     |1                        |EPOCH of 01-Jan-1970 00:00:00|
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|Themis Peer        |VARNAME_time                |sec                 |TIME            |UT                 |Same as time var name|UTC, in seconds sinc 01-Jan-1970 00:00:00|CDF_DOUBLE          |                     |> data                |Unleaped seconds|
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|Themis Peer        |VARNAME_epoch            |field missing |0                   |UT                 |Same as time var name|VARNAME                                                            |CDF_EPOCH            |                     |normal              |field missing|
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|Themis Peer        |VARNAME_epoch0          |msec              |EPOCH0    |timebase      |Same as time var name|EPOCH of THEMIS time base                           |CDF_EPOCH           |                     |1                        |EPOCH of 01-Jan-1970 00:00:00|
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|MMS fpi                |Epoch (absent, Epoch_minus_var is present)          |s                 |0                   |Field missing                 | VARNAME|VARNAME                      |CDF_UINT1               |                     |1                         |VARNAME|
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|MMS scm             |epoch_timetag                   |ns                   |0                   |VARNAME   |Same as time var name|Packet time time                                                  |CDF_TIME_TT2000|                     |normal               |field missing|
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|MMS scm             |Epoch  (other var time)     |ns                   |0                   |VARNAME   |Same as time var name|Time                                                                       |CDF_TIME_TT2000|                     |normal               |field missing|
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|ACE mfi                |Epoch                                   |ms                 |0                   |VARNAME   |Time                                  |Time  ,beginning of interval                               |CDF_EPOCH           |                     |normal               |field missing|
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|Helios nessmag |Epoch                                   |ms                 |0                   |field missing |Epoch                               |Default Time                                                         |CDF_EPOCH           |                     |normal               |field missing|
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|Ulysses hft           |Epoch                                   |ms                 |0                   |Time               |Epoch                               |Time in NSSDC Epoch format                         |CDF_EPOCH           |                     |normal               |field missing|
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|SOHO cst             |Epoch                                   |ms                 |0                   |Epoch            |Time Line                         |Time                                                                     |CDF_EPOCH           |                     |normal               |field missing|
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h2. Algorithm Proposition
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VariableThatNeedsTime
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depend0 = get(VariableThatNeedsTime.DEPEND_0 variable)
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if(depend0.nbOfRec == VariableThatNeedsTime.nbOfRec)
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* test depend0.firstValue for different double range mentionned above (this part might include CDF_TYPE for TT2000)
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* if(ambiguity)
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** look at depend0.units
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** if field is missing, look at VariableThatNeedsTime.depend_epoch0.units field  
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//ATM, these lines are written, epoch0 units are useless since that variable only appears when matching time is DEPEND_TIME variable
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else
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dependTime = get(VariableThatNeedsTime.DEPEND_TIME variable)
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if(dependTime.nbOfRec == VariableThatNeedsTime.nbOfRec)
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* test dependTime.firstValue for different double range mentionned above (this part might include CDF_TYPE for TT2000)
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* if(ambiguity)
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** look at dependTime.units
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h2. Useful links
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http://spdf.gsfc.nasa.gov/CDFconversion/time_formats.html
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http://cdf.gsfc.nasa.gov/html/leapseconds_requirements.html
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how autoplot is processing cdf files :
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http://autoplot.org/help#Reading_CDF