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Message ID: 14632     Entry time: Thu May 23 08:51:30 2019
Author: Milind 
Type: Update 
Category: Cameras 
Subject: Setting up beam spot simulation 

I have done the following thus far since elog #14626:

Simulation:

  1. Cleaned up Pooja's code for simulating the beam spot. Added extensive comments and made the code modular. Simulated the Gaussian beam spot to exhibit 
    1. Horizontal motion
    2. Vertical motion
    3. motion along both x and y directions:
  2. The motion exhibited in any direction in the above videos is the combination of four sinusoids at the frequencies: 0.2, 0.4, 0.1, 0.3 Hz with amplitudes that can be found as defaults in the script ((0.1, 0.04, 0.05, 0.08)*64 for these simulations.). The variation looks as shown in Attachment 1. For the sake of convenience I have created the above video files with only a hundred frames (fps = 10, total time ~ 10s) and this took around 2.4s to write. Longer files need much longer. As I wish to simply perform image processing on these frames immediately, I don't see the need to obtain long video files right away.
  3. I have yet to add noise at the image level and randomness to the motion itself.  I intend to do that right away. Currently video 3 will show you that even though the time variation of the coordinates of the center of the beam is sinusoidal, the motion of the beam spot itself is along a line as both x and y motions have the same phase. I intend to add the feature of phase between the motion of x and y coordinates of the center of the beam, but it doesn't seem all too important to me right now. The white margins in the videos generated are annoying and make tracking the beam spot itself slightly difficult as they introduce offset (see below). I shall fix them later if simple cropping doesn't do the trick.
  4. I have yet to push the code to git. I will do that once I've incorporated the changes in (3).

Circle detection:

  1. If the beam spot intensity variation is indeed Gaussian (as it definitely is in the simulation), then the contours are circular. Consequently, centroid detection of the beam spot reduces to detecting these contours and then finding their centroid (center). I tried this for a simulated video I found in elog post 14005. It was a quick implementation of the following sequence of operations: threshold (arbritrarily set to 127), contour detection (video dependent and needs to be done manually), centroid determination from the required contour.  Its evident that the beam spot is being tracked (green circle in the video). Check #Attachment 2 for the results. However, no other quantitative claims can be made in the absence of other data.
  2. Following this, Gautam pointed me to a capture in elog post 13908. Again, the steps mentioned in (1) were followed and the results are presented below in Attachment #3. However, this time the contour is no longer circular but distorted. I didn't pursue this further. This test was just done to check that this approach does extend (even if not seamlessly) to real data. I'm really looking forward to trying this with this real data.
  3. So far, the problem has been that there is no source data to compare the tracked centroid with. That ought to be resolved with the use of simulated data that I've generated above. As mentioned before, some matplotlib features such as saving with margins introduce offsets in the tracked beam position. However, I expect to still be able to see the same sinusoidal motion. As a quick test, I'll obtain the fft of the centroid position time series data and check if the expected frequencies are present.

I will wrap up the simulation code today and proceed to going through Gabriele's repo. I will also test if the contour detection method works with the simulated data. During our meeting, it was pointed out that when working with real data, care has to be taken to synchronize the data with the video obtained. However, I wish to put off working on that till later in the pipeline as I think it doesn't affect the algorithm being used. I hope that's alright (?).

 

Attachment 1: variation.pdf  13 kB  Uploaded Thu May 23 11:12:04 2019  | Hide | Hide all
variation.pdf
Attachment 2: contours_simulated.mp4  625 kB  Uploaded Thu May 23 12:13:49 2019
Attachment 3: contours_real.mp4  12.113 MB  Uploaded Thu May 23 12:21:44 2019
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