====== linearisePhi.m =====

**Class:** Function

**Description:** Calculates and inserts the fullPhi field of [[usage:tracking#outputs|procTracks]]. fullPhi is based on phi, but has had increments of 180 degrees added and subtracted to allow you to smoothly keep track of a single pole.

**Author:** Oliver J. Meacock

<code matlab linearisePhi.m>

function procTracks = linearisePhi(procTracks)
%LINEARISEPHI takes the phi field of the input version of procTracks
%(defined nematically, so between -90 and 90) and adds or subtracts
%increments of 180 to each position in the track to ensure phi keeps track
%of a single pole.
%
%   INPUTS:
%       procTracks: The output of the tracking module of FAST, stored in
%       the 'Tracks.mat' file.
%
%   OUTPUTS:
%       procTracks: Version of procTracks with a new 'fullPhi' field, which
%       contains the wrapped version of phi.
%
%   Author: Oliver J. Meacock, (c) 2019

for i = 1:size(procTracks,2)
    phiDiff = diff(procTracks(i).phi);
    stepsUp = phiDiff < -90;
    stepsDown = phiDiff > 90;
    intSteps = cumsum(stepsUp - stepsDown);
    intSteps = [0; intSteps];
    procTracks(i).fullPhi = procTracks(i).phi + intSteps*180;
end

</code>

**Example usage:**

<code matlab>
  %Apply the linearisePhi function to a given procTracks structure
  procTracks = linearisePhi(procTracks);
  
  %Plot phi before and after linearisation
  plot(procTracks(155).phi)
  hold on
  plot(procTracks(155).fullPhi)
  
  xlabel('Time')
  ylabel('Phi (degrees)')
  
  legend('phi','fullPhi')
</code>
 
**Example output:** 

{{ :post:linearisephitest.png?400 }}