A Measurement is a cluster that has been assigned to a TrackTrack. It should contain a measure and a covariance. A measurement should be able to give fast access to chi2, residual and residual error. It should also know which type of cluster it originated from. For refitting purpose the measurement should have access to geometry information.


  • In order to provide a measurement error the Velo R, Phi measurements need as input the TrackTrajectory
  • The outer tracker measurement includes the Left/Right ambiguity as assigned by pattern recognition

Discussion points:

  • The TrackMeasurements can only be 1-dimensional. This has consequences for the use of 2-dimensional measurements:
    • It is assumed that a 2-D measurement can be decomposed into two independent measurements. E.g. a "pad" measurement is treated correctly as long as the pad is rectangular.
    • The beamspot with an elliptical shape cannot be treated exact
    • The r and phi strips cannot be treated as "pads", but only as 1-d measurements

-- MarcelMerk - 07 Apr 2005

Velo R clusters

These are calculated as the local radius of the strip and the phi of the current track projection. The meausrement becomes

  • the angle of line of the tangent to the circle at that point
  • the radius of the cluster + width of cluster
The measurement is then moved into the global frame in the full fit. The measurement must be recalculated each time the track projection moves.

The track position is then the distance of the track point to the line and is compared to the measurement value.

See diagram below.

Velo phi clusters

These are taken as the

  • The angle of the line defining the strip
  • The d0, distance of closest approach to the origin, plus width of cluster
The meausrement is moved into the global frame, as the measurement is independant of the track position this is only done once.

The track position is then the distance of the track point to the line and is compared to the measurement value.

Note the sign of d0 is important as this determines which side of the origin the measurement is.

See diagram below.

-- DavidHutchcroft - 18 Aug 2005

  • Graphic of how Velo Measurements are used:
    Graphic of how Velo Measurements are used
Topic attachments
I Attachment History Action Size Date Who Comment
Unknown file formateps AlignVeloMeasurments.eps r1 manage 290.0 K 2005-08-18 - 16:22 DavidHutchcroftSecondary Graphic of how Velo Measurements are used
PNGpng AlignVeloMeasurments.png r1 manage 14.4 K 2005-08-18 - 16:25 DavidHutchcroftSecondary Graphic of how Velo Measurements are used
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Topic revision: r6 - 2005-08-18 - DavidHutchcroftSecondary
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