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PHUNWRAP

PHUNWRAP

Name


  PHUNWRAP

Author


  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
  craigm@lheamail.gsfc.nasa.gov
  UPDATED VERSIONs can be found on my WEB PAGE:
      http://cow.physics.wisc.edu/~craigm/idl/idl.html

Purpose


  Unwrap phase jumps to recover cycle counts

Major Topics


  Mathematics

Calling Sequence


  CYCLES = PHUNWRAP(PHASE, TOLERANCE=, MAXVAL=)

Description



  PHUNWRAP unwraps a sequence of phases to produce a new series of
  cycle counts. Phase jumps due to crossing over the PHASE=0
  boundary are removed by adding an integral number of cycles. The
  algorithm is based on the MATLAB "unwrap" function.
  NOTE: the unwrapping process can be ambiguous if there is a phase
  jump of more than a half cycle in the series. For example, if the
  phase changes by ~0.5 cycles, it is not possible to distinguish
  whether there wasa +0.5 cycle or -0.5 cycle jump. The most
  accurate unwrapping can be performed if the PHASE series is nearly
  continuous and does not have rapid phase changes.
  Users can select the tolerance used to determine the phase jump.
  Users can also select the definition of "1 cycle" by changing
  MAXVAL. By default, MAXVAL is 2*!DPI, which correspondes to 1
  cycle = 2*!DPI radians, but other values of 1 (cycle), or 360
  (degrees) are possible.

Inputs



  PHASE - phase series to be unwrapped. Values should range from 0
          to MAXVAL. The ordering of the series is important.

Returns



  A new series, expressed in cycles, with cycle jumps larger than
  TOLERANCE removed.

Optional Keywords



  TOLERANCE - phase jump tolerance. If the phase from one sample to
              the next changes by more than TOLERANCE, then a single
              cycle jump is assumed to have occurred.
              DEFAULT: 0.5*MAXVAL
  MAXVAL - Maximum value for phase. Common values are: 2*!DPI
            (radians; DEFAULT); 1 (cycle); 360 (degrees), but any
            positive value may be used.

Example



  ;; Set up some fake data
  x = dindgen(100)/10d
  y = x/2
  ph = y MOD 1.0 ;; Mock phases
  cycles = phunwrap(ph, maxval=1)

Modification History


  Written and documented, CM, July 2003
  Handle the case of unsigned integer input, CM, Feb 2006
  $Id: phunwrap.pro,v 1.3 2006/03/28 14:19:53 craigm Exp $



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