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feat: iterate on SsfStepDetector

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* use SSF signal instead of accelerometer signal
* use higher BEAT_CORR_THR_{12} for SSF signal
* add absolute SSF_THRESHOLD to ignore small accelero bumps
* compute ssf_threshold according to detected SSF peaks, not the mean (more robust vs. noise)
This commit is contained in:
David Madl
2026-03-11 20:47:53 +01:00
parent 95d1fee44d
commit 90f8943930
8 changed files with 103 additions and 27 deletions
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33
pasada-lib/ssf_filter.cpp
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@@ -6,6 +6,7 @@
#include <limits>
#include <cmath>
#include <cassert>
#include <iostream>
static std::vector<double> make_ones(size_t sw) {
std::vector<double> ones;
@@ -33,21 +34,26 @@ SsfStepDetector::SsfStepDetector(size_t len_refr) :
LEN_TH_WIN((size_t) (3.0 * FPS)), // subsequent window length for ssf_threshold
num_samples(0),
ssf_threshold(std::numeric_limits<double>::infinity()),
ssf_threshold_nm1(std::numeric_limits<double>::infinity()),
f_ssf_threshold_smoothing(6, 0, 0, make_ones(6)),
len_refr(len_refr), n_refr(0), is_refr(false),
nm1_ssf(0.0),
ssf_nm1(0.0),
f_ssf_mean(LEN_TH_WIN, 0, 0, make_ones(LEN_TH_WIN))
{
assert (LEN_INIT >= LEN_TH_WIN && "LEN_INIT < LEN_TH_WIN, check normalization of initial ssf_threshold");
}
double SsfStepDetector::filter(double val) {
double ssf_mean = f_ssf_mean.filter(val) / ((double) LEN_TH_WIN);
double SsfStepDetector::filter(double ssf) {
double ssf_mean = f_ssf_mean.filter(ssf) / ((double) LEN_TH_WIN);
double rv = 0.0;
if (num_samples >= LEN_INIT) {
// initial and subsequent threshold setting.
ssf_threshold = 3.0 * ssf_mean * 0.99; // see Zong 2003 for the magic numbers
}
// threshold crossing detection
bool is_txing = nm1_ssf < ssf_threshold && val >= ssf_threshold;
// 'is_prev_lower' fixes a glitch where a falling threshold leads to undetected crossings
bool is_prev_lower = ssf_nm1 < ssf_threshold || ssf_nm1 < ssf_threshold_nm1;
bool is_cur_higher = ssf >= ssf_threshold;
bool is_txing = is_prev_lower && is_cur_higher;
// refractory period reset
if (num_samples - n_refr >= len_refr) is_refr = false;
// transition and not in refractory period? detected a step.
@@ -56,7 +62,24 @@ double SsfStepDetector::filter(double val) {
is_refr = true;
n_refr = num_samples;
}
nm1_ssf = val;
if (num_samples == LEN_INIT) {
// initial threshold setting
ssf_threshold = 3.0 * ssf_mean * 0.99; // see Zong 2003 for the magic numbers
//std::cerr << "before prime()" << std::endl;
f_ssf_threshold_smoothing.prime(ssf_threshold);
} else if (num_samples > LEN_TH_WIN) {
//std::cerr << "adaptive threshold setting" << std::endl;
// adaptive threshold setting
// +2 is half the window size
// TODO: param upon SsfFilter.upslope_width/2 instead of hardcoding -- also f_ssf_threshold_smoothing(), nb. should be even number
if (num_samples == n_refr + 2) {
//std::cerr << "setting adaptive threshold setting" << std::endl;
ssf_threshold_nm1 = ssf_threshold;
// the ssf peak comes 3 samples (half-window + 1 sample) after the crossing
ssf_threshold = f_ssf_threshold_smoothing.filter(ssf) / ((double) f_ssf_threshold_smoothing.size()) * 0.6;
}
}
ssf_nm1 = ssf;
num_samples++;
return rv;
}