Push the data through a low-pass filter: 
use constant {
    alpha   => 0.1,
};

my ($prev_x, $prev_y) = (0, 0);
while (<>) {
    my ($t, $x, $y) = split;

    $x = $prev_x + alpha * ($x - $prev_x);
    $prev_x = $x;

    $y = $prev_y + alpha * ($y - $prev_y);
    $prev_y = $y;

    print "$t $x $y\n";
}

[download]
Tweak the alpha to get at the desired frequency band.

In reply to Re: Finding local maxima/minima in noisy, pediodic data by mpeg4codec
in thread Finding local maxima/minima in noisy, pediodic data by kikuchiyo

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