feat: add GravityFilter and Resampler to StepDetector

google-tests/test4.cpp

@@ -20,12 +20,13 @@ TEST(StepDetector, t1_sub_sample_resolution) {
     StepDetector det(fps, nullptr, true);
 
     // initialize: feed for priming the filters
-    det.primeFilters(fps, signal);
+    double ts = det.primeFilters(fps, signal);
 
     // feed for actual test
     for (size_t i = 0; i < N; i++) {
         const auto a_i = static_cast<float>(signal[i]);
-        det.filter(std::vector<float> {0.0f, a_i, 0.0f});
+        det.filter(ts, std::vector<float> {0.0f, a_i, 0.0f});
+        ts += 1.0 / fps;
     }
 
     std::vector<double> ssd = det.getBufSsd(); // raw SsfStepDetector

pasada-lib/include/pd_signal.h

@@ -44,6 +44,8 @@ namespace pd_signal {
     double mean(const std::vector<double>& in);
     void diff(std::vector<double>& out, const std::vector<double>& in);
 
+    std::vector<double> gauss(size_t N, double mu, double sigma);
+
     /**
      * Convolution of two polynomials given in ASCENDING power order.
      * If <c>p = p_0 + p_1 x + ... + p_{P-1} x^{P-1}</c> and likewise for q,

pasada-lib/include/step_detector.h

@@ -7,6 +7,7 @@
 
 #include "iir_filter.h"
 #include "ssf_filter.h"
+#include "pd_resamp.h"
 #include <vector>
 
 class StepListener {
@@ -15,6 +16,19 @@ public:
     virtual void playBeat() = 0;
 };
 
+/** mean-filter the gravity vector, then take acceleration downwards */
+class GravityFilter {
+    size_t N;
+    std::vector<double> gauss_taps;
+    Filt gx;
+    Filt gy;
+    Filt gz;
+public:
+    // 5 secs buffer, prime y with direction of gravity (for tests & faster init)
+    GravityFilter(double fps);
+    double filter(std::vector<double> values);
+};
+
 /**
  * Step detector from accelerometer signal.
  *
@@ -24,7 +38,7 @@ public:
 class StepDetector {
 protected:
     StepListener *listener;
-    Filt f_neg;
+    GravityFilter f_grav;
     SsfFilter f_ssf;
     SsfStepDetector f_ssd;
     RunningQualityFilter f_sqi;
@@ -34,9 +48,14 @@ protected:
     std::vector<double> buf_sqi;
     std::vector<double> buf_out;
 
+    Resampler res_x;
+    Resampler res_y;
+    Resampler res_z;
+
 public:
     StepDetector(double fps, StepListener *listener, bool debug = false);
-    void filter(std::vector<float> values);
+    void filter(double ts, std::vector<float> values);
+    void filter_a(double s1);
     std::vector<double> getBufSsd();
     std::vector<double> getBufSqi();
     std::vector<double> getBufOut();
@@ -45,7 +64,7 @@ public:
      * Prime the filters using the given input signal.
      * Used for debugging (non-realtime processing) to align the signal.
      */
-    void primeFilters(double fps, std::vector<double> sig);
+    double primeFilters(double fps, std::vector<double> sig);
 };
 
 #endif //PASADASUPERPROJECT_STEP_DETECTOR_H

pasada-lib/pd_signal.cpp

@@ -161,6 +161,16 @@ void diff(std::vector<double>& out, const std::vector<double>& in) {
     }
 }
 
+std::vector<double> gauss(size_t N, double mu, double sigma) {
+    const double norm = sigma * sqrt(2.0 * kPi);
+    std::vector<double> data(N);
+    for (int i = 0; i < N; i++) {
+        const double x = i;
+        data[i] = std::exp(-0.5 * (x - mu) * (x - mu) / (sigma * sigma)) / norm;
+    }
+    return data;
+}
+
 // Convolution of two polynomials in ascending power order.
 void polymul(std::vector<cplx>& out,
              const std::vector<cplx>& p, const std::vector<cplx>& q) {

pasada-lib/step_detector.cpp

@@ -4,19 +4,63 @@
 
 #include "step_detector.h"
 
+#include "pd_signal.h"
+
 StepDetector::StepDetector(double fps, StepListener *listener, bool debug) :
     listener(listener),
-    f_neg(1, 0, 0, std::vector<double> {-1.0}),
+    f_grav(fps),
     f_ssf(fps),
     f_ssd(fps),
     f_sqi(fps),
     debug(debug)
 {}
 
-void StepDetector::filter(std::vector<float> values) {
+static int gravity_num_taps(double fps) {
-    // TODO: later on, we should use a vector projection towards gravity
+    return 5.0 * fps;
-    auto s1 = (double) values[1]; // take y-axis value for now
+}
-    auto s2 = f_neg.filter(s1);
+
+// 5 secs buffer, prime y with direction of gravity (for tests & faster init)
+GravityFilter::GravityFilter(double fps) :
+    N(gravity_num_taps(fps)),
+    gauss_taps(pd_signal::gauss(N, N/2, N/4)),
+    gx(N, 0, 0, gauss_taps),
+    gy(N, 0, 0, gauss_taps),
+    gz(N, 0, 0, gauss_taps)
+{
+    gy.prime(-9.81);
+}
+
+double GravityFilter::filter(std::vector<double> values) {
+    gx.push(values[0]);
+    gy.push(values[1]);
+    gz.push(values[2]);
+    double x = gx.peek(), y = gy.peek(), z = gz.peek();
+    double g = sqrt(x * x + y * y + z * z);
+    // e = mean(a)
+    double ex = x / g, ey = y / g, ez = z / g;
+    // e \in a
+    double vx = values[0] * ex;
+    double vy = values[1] * ey;
+    double vz = values[2] * ez;
+    return vx + vy + vz;
+}
+
+void StepDetector::filter(double ts, std::vector<float> values) {
+    // resample to smooth over Android sensor FPS variations
+    res_x.push(ts, values[0]);
+    res_y.push(ts, values[1]);
+    res_z.push(ts, values[2]);
+    while (res_x.peek()) {
+        double x = res_x.get(), y = res_y.get(), z = res_z.get();
+        std::vector<double> samp { x, y, z };
+        // gravity filtering
+        double a = f_grav.filter(samp);
+        // pass on accel sample
+        filter_a(a);
+    }
+}
+
+void StepDetector::filter_a(double s2) {
     auto s3 = f_ssf.filter(s2);
     auto s4 = f_ssd.filter(s3);
     auto q5 = f_sqi.filter(s2, s3, s4);
@@ -35,15 +79,18 @@ std::vector<double> StepDetector::getBufSsd() { return buf_ssd; }
 std::vector<double> StepDetector::getBufSqi() { return buf_sqi; }
 std::vector<double> StepDetector::getBufOut() { return buf_out; }
 
-void StepDetector::primeFilters(double fps, std::vector<double> sig) {
+double StepDetector::primeFilters(double fps, std::vector<double> sig) {
     const size_t N_INIT = SsfStepDetector::initial_samples(fps);
     // initialize: feed for priming the filters
+    double ts = 0;
     for (size_t i = 0; i < N_INIT; i++) {
         const auto a_i = static_cast<float>(sig[i]);
-        filter(std::vector<float> {0.0f, a_i, 0.0f});
+        filter(ts, std::vector<float> {0.0f, a_i, 0.0f});
+        ts += 1.0 / fps;
     }
     // clear debug buffers
     buf_ssd.clear();
     buf_sqi.clear();
     buf_out.clear();
+    return ts;
 }