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Fixing sweep durations that cause weird tracker behaviour

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    The tracker plugin requires that the duration of each sweep be accurately known, otherwise it can generate
    spurious tracks and misconnect new blips to existing tracks.  This problem sometimes appears in blipmovies
    generated by converting RTI .REC files (the source is the issue is under investigation).

    The highlighted track in the screenshot below is an example of such a misconnection:

    is an

    On a typical radar spinning at 25 rpm, the sweep duration is 2.4 seconds.  In blipmovies, this value is available from the R console like so:


    The value is in milliseconds, so for a typical radar, the value should be around 2400.  The value for the
    sweep shown above was 214798 milliseconds, which is obviously very wrong.

    If you see strange behaviour in the tracker, especially sudden misconnections among existing tracks,
    or long new segments attached to previously reasonable tracks, your blipmovie might have (occasional)
    sweep duration errors.  If you suspect this, try paste the following into your radR console window, then
    run the tracker on the suspect portion of a blipmovie.  If the results in the console window include values
    very different from 2400, then you should correct the blipmovie (see below).

    rss.add.hook("DONE_SCAN", function(...) gui.put.cons(paste("Sweep at", capture.output(round(RSS$scan.info$timestamp)), "is", round(RSS$scan.info$duration), "milliseconds\n")))

    Here's the result from a blipmovie segment with bad durations (one of which is highlighted):

    Fixing blipmovies with bad sweep durations

    These movies can be fixed by a new script which is available here (and will be included in future releases of radR).

    Before running the script on any blipmovies, make sure to make backup copies of both the ".bm" and the ".bm.i" files!

    To run the script, right-click in the radR plot window and choose "Source an R script...",
    then navigate to the radR/scripts folder and select fix_blipmovie_sweep_durations.R

    The script will prompt you for a folder.  All blipmovies in that folder and in any subfolders will have their sweep durations
    corrected by using the top-of-sweep timestamps to recalculate them.  This will increase the size of each .bm and .bm.i file
    by around 0.5% or less, so make sure you have at least a little bit of spare disk space on the drive where the blipmovies reside.

    Note: of course, this script relies on accurate sweep timestamps.  If you don't have those, you already have more
    serious issues!

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    this script recalculates sweep durations in every blipmovie in a user-selected folder. Save it in your radR/scripts folder.
    3.51 kB14:25, 6 Sep 2013JohnActions
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