perturb_points_cps

 ==============================================================
 PERTURB_POINTS_CPS: Perturbs the points in an image using Clamped-Plate
                     Spline warps.

 Code written by Katherine Smith, 2003

    GENERAL

      points = perturb_points_cps(points, error)

    INPUT/S

      -points:
           The points in their original (initial) position.

      -error:
           Controls the perturbation weight.
           
    OUTPUT/S

      -points:
           The points after they have been perturbed.

    PENDING WORK

      -

    KNOWN BUG/S

      -None.

    COMMENT/S

      -Performs several warps so might be slow.

    RELATED FUNCTION/S

      

    ABOUT

      -Created:     November 23rd, 2003
      -Last update: Novermber 26th, 2003
      -Revision:    0.0.2
      -Author:      R. S. Schestowitz, University of Manchester
 ==============================================================

0001 function points = perturb_points_cps(points, error)
0002 % ==============================================================
0003 % PERTURB_POINTS_CPS: Perturbs the points in an image using Clamped-Plate
0004 %                     Spline warps.
0005 %
0006 % Code written by Katherine Smith, 2003
0007 %
0008 %    GENERAL
0009 %
0010 %      points = perturb_points_cps(points, error)
0011 %
0012 %    INPUT/S
0013 %
0014 %      -points:
0015 %           The points in their original (initial) position.
0016 %
0017 %      -error:
0018 %           Controls the perturbation weight.
0019 %
0020 %    OUTPUT/S
0021 %
0022 %      -points:
0023 %           The points after they have been perturbed.
0024 %
0025 %    PENDING WORK
0026 %
0027 %      -
0028 %
0029 %    KNOWN BUG/S
0030 %
0031 %      -None.
0032 %
0033 %    COMMENT/S
0034 %
0035 %      -Performs several warps so might be slow.
0036 %
0037 %    RELATED FUNCTION/S
0038 %
0039 %
0040 %
0041 %    ABOUT
0042 %
0043 %      -Created:     November 23rd, 2003
0044 %      -Last update: Novermber 26th, 2003
0045 %      -Revision:    0.0.2
0046 %      -Author:      R. S. Schestowitz, University of Manchester
0047 % ==============================================================
0048 
0049 % slap some random warps down
0050 % don't warp the first or the last
0051 
0052 n_warps = 5; 
0053              % number of warps??
0054 interval = (max(points)-min(points))/n_warps;
0055              % interval is the margin between maxima and minima divided
0056              % by the number of warps??
0057 max_shift = error * 0.67 * (interval/2);
0058              % maximum shift is guided by error value multiplied
0059              % by mysterious numbers
0060 for i = 0:n_warps-1;
0061              % for all warps (0-4 inclusive)
0062   warp_centre = min(points) + i*interval + interval/2;
0063              % set some centre
0064   shift = rand * max_shift;
0065   shift = shift/(interval/2-1);
0066              % should say: (rand * max_shift)/(interval/2-1);
0067              % What does that mean in practice?
0068   points = cps_warp_1d(points, warp_centre, interval/2-1, shift);
0069             % apply a clamped-plate spline warp
0070 end