ITK Release 4/Video/Time Stamp

From KitwarePublic
Jump to navigationJump to search

Reference Systems

VRPN - UNC

URL

http://www.cs.unc.edu/Research/vrpn/vrpn_getting_started.html

Time Stamp Structure

<source lang="cpp"> struct timeval 

 {
   __time_t tv_sec;		/* Seconds.  */
   __suseconds_t tv_usec;	/* Microseconds.  */
 };

</source>

OpenCV

  • include/opencv/cv.h: double timestamp
  • src/cv/_cvipp.h: float timestamp
  • 3rdparty/include/ffmpeg_/avformat.h: int64_t timestamp;

KWSys

  • static double GetTime();

ITK RealTimeClock

System Time

Scales

If counting from a given starting point (forward):


  • int32 : can count in microseconds, up to 4.5 years
    • 2**32 / (30 * 3600 * 24.0 * 365 ) = 4.5 years
  • double : can count in microseconds, up to 285 years (before losing any precision)
    • 2^53 / ( 1000000 * 3600 * 24.0 * 365 ) = 285
    • after that it will be counting in tens of microseconds...
  • int64 : can count in microseconds, up to 584942 years
    • 2**64 / ( 1000000 * 3600 * 24.0 * 365 ) = 584942
    • (or in nanoseconds up to 584 years)


If counting relative times:

  • int32 -> will use the sign, and can count (-2.4, +2.4) years
  • double -> and can count (-142, +142) years
  • int64 -> (-292471, +292471) years

Units

  • Should the time units be specified ?
    • Use microseconds ?

Proposal

  • Use double as internal representation
  • Use micro-seconds as unit
  • Have convenience methods to return time in other units
    • seconds, hours, days
  • Have convenience methods for computing differences between two times
  • Encapsulated type:
    • External time representation = double in microseconds
    • Internal time representation is private and is not exposed
  • Two Classes
    • TimeStamp
    • TimeInterval
    • TimeInterval = TimeStamp - TimeStamp
    • TimeStamp = TimeStamp + TimeInterval
    • Time operations will be implemented in these two classes.
    • They will have to be as efficient as double or int64 arithmetics.
  • "Get" methods only available for debugging
    • TimeStamp.GetTimeInSecondsSince1970();
  • Serialization
    • ostream<< (controlled by ITK)
    • when sent to file formats then we will be subject to the file format representation (just as we are with images).
Retrieved from "https://public.kitware.com/Wiki/index.php?title=ITK_Release_4/Video/Time_Stamp&oldid=34928"