Difference between revisions of "OpenIGTLink/Timestamp"

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[[OpenIGTLink | << OpenIGTLink]]
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[[OpenIGTLink | << OpenIGTLink]] | [[OpenIGTLink/Protocol | Protocol]]
  
  
NTP4 Timestamp is defined by [http://www.faqs.org/rfcs/rfc2030.html RFC 2030] and [http://www.faqs.org/rfcs/rfc1305.html RFC 1305]. (See "3. NTP Timestamp Format")
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'''Big Endian format:''' bits numbered in big-endian fashion from 0 starting at the left, or high-order, position.
  
'''Big Endian format:''' NTP data are specified as integer or fixed-point
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'''Seconds and fraction of seconds:''' timestamps are represented as a 64-bit unsigned
quantities, with bits numbered in big-endian fashion from 0 starting
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fixed-point number, in seconds relative to 00:00:00 January 1, 1970, UTC. The
at the left, or high-order, position.
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integer part is in the first 32 bits (Unix-style timestamp) and the fraction part in the
 
 
'''Seconds and fraction of seconds:''' NTP timestamps are represented as a 64-bit unsigned
 
fixed-point number, in seconds relative to 0h on 1 January 1900. The
 
integer part is in the first 32 bits and the fraction part in the
 
 
last 32 bits. In the fraction part, the non-significant low order can
 
last 32 bits. In the fraction part, the non-significant low order can
 
be set to 0.
 
be set to 0.
  
'''Convention:''' Note that, since some time in 1968 (second 2,147,483,648) the most
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'''Wrap around:''' The first 32-bit field will overflow some time in 2106 (second 4,294,967,296)
significant bit (bit 0 of the integer part) has been set and that the
 
64-bit field will overflow some time in 2036 (second 4,294,967,296).
 
There will exist a 232-picosecond interval, henceforth ignored, every
 
136 years when the 64-bit field will be 0, which by convention is
 
interpreted as an invalid or unavailable timestamp.
 
 
 
If bit 0 is set, the UTC time is in the range 1968-2036 and UTC time
 
is reckoned from 0h 0m 0s UTC on 1 January 1900.  If bit 0 is not
 
set, the time is in the range 2036-2104 and UTC time is calculated
 
from 6h 28m 16s UTC on 7 February 2036.  Note that when calculating
 
the correspondence, 2000 is a leap year and leap seconds are not
 
included in the reckoning.
 
 
 
'''Precision:''' 200 picoseconds
 
 
 
'''Wrap around:''' in year 2104
 
  
 
== Obtaining timestamp ==
 
== Obtaining timestamp ==
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* [http://www.itk.org/Doxygen34/html/classitk_1_1RealTimeClock.html itk::RealTimeClock]
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* '''Linux''' / '''Mac''': [http://www.hmug.org/man/3/ftime.php ftime()]
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* '''Windows''': [http://msdn2.microsoft.com/en-us/library/z54t9z5f(VS.71).aspx ftime()] - 10 ms resolution
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** '''Old Timestamp''' - 1 sec resoultion: Now, [http://msdn2.microsoft.com/en-us/library/1f4c8f33.aspx Time], Timer
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** '''System time''' - 10 msec resolution: GetTickCount, [http://msdn2.microsoft.com/en-us/library/ms724411.aspx GetTickCount64] or [http://msdn2.microsoft.com/en-us/library/ms713418(VS.85).aspx timeGetTime()]
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** '''Highres''' - hardware dependent: [http://msdn2.microsoft.com/en-us/library/ms644904.aspx QueryPerformanceCounter] (Intel IA32 instruction: [http://www.intel.com/design/pentium4/manuals/245471.htm RDTSC])
  
Intel IA32 instruction [http://www.intel.com/design/pentium4/manuals/245471.htm RDTSC]
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== Time synchronization ==
* '''Windows:''' Use [http://msdn2.microsoft.com/en-us/library/ms644904.aspx QueryPerformanceCounter()] or [http://msdn2.microsoft.com/en-us/library/ms713418(VS.85).aspx timeGetTime()] (10ms)
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Two solutions:
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# Install NTP on all devices
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# Compute timestamp differences (local NTP can be used)
  
== Calibrating the counters ==
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== Resources ==
# Install NTP or compute timestamp differences
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* NTP4 Timestamp: [http://www.faqs.org/rfcs/rfc2030.html RFC 2030] and [http://www.faqs.org/rfcs/rfc1305.html RFC 1305]. (See "3. NTP Timestamp Format")
# Calibrate timestamp (counter) - real time difference
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* [http://www.lochan.org/2005/keith-cl/useful/win32time.html Obtaining Accurate Timestamps under Windows XP]

Latest revision as of 21:58, 11 February 2008

Home < OpenIGTLink < Timestamp

<< OpenIGTLink | Protocol


Big Endian format: bits numbered in big-endian fashion from 0 starting at the left, or high-order, position.

Seconds and fraction of seconds: timestamps are represented as a 64-bit unsigned fixed-point number, in seconds relative to 00:00:00 January 1, 1970, UTC. The integer part is in the first 32 bits (Unix-style timestamp) and the fraction part in the last 32 bits. In the fraction part, the non-significant low order can be set to 0.

Wrap around: The first 32-bit field will overflow some time in 2106 (second 4,294,967,296)

Obtaining timestamp

Time synchronization

Two solutions:

  1. Install NTP on all devices
  2. Compute timestamp differences (local NTP can be used)

Resources