--- /dev/null
+/*
+ * Kaiser Window digital filter
+ *
+ * Copyright © 2001, Keith Packard
+ * All Rights Reserved. See the file COPYING in this directory
+ * for licensing information.
+ */
+
+real i0(real x)
+{
+ real ds, d, s;
+
+ ds = 1;
+ d = 0;
+ s = 0;
+ do
+ {
+ d = d + 2;
+ ds = ds * x**2 / d**2;
+ s = s + ds;
+# printf ("ds %g s %g dist %g\n", ds, s,
+# ds - 0.2e-8 * s);
+ }
+ while (ds - 0.2e-8 * s > 0);
+ return s;
+}
+
+real highpass (real n, real m, real wc)
+{
+ real alpha = m/2;
+ real dist;
+
+ dist = n - alpha;
+ if (dist == 0)
+ return (pi/2 - wc) / pi;
+ return -sin(dist * (pi/2-wc)) / (pi * dist);
+}
+
+real lowpass (real n, real m, real wc)
+{
+ real alpha = m/2;
+ real dist;
+ dist = n - alpha;
+ if (dist == 0)
+ return wc / pi;
+ return sin (wc * dist) / (pi * dist);
+}
+
+real kaiser (real n, real m, real beta)
+{
+ real alpha = m / 2;
+ return i0 (beta * sqrt (1 - ((n - alpha) / alpha)**2)) / i0(beta);
+}
+
+void write_high (string filename,
+ real m,
+ real wc,
+ real beta,
+ real step)
+{
+ real n;
+ file f;
+
+ f = File::open (filename, "w");
+ for (n = 0; n <= m; n += step)
+ File::fprintf (f, "%g,\n", highpass (n, m, wc) * kaiser (n, m, beta));
+ File::close (f);
+}
+
+void write_low (string filename,
+ real m,
+ real wc,
+ real beta,
+ real step)
+{
+ real n;
+ file f;
+
+ f = File::open (filename, "w");
+ for (n = 0; n <= m; n += step)
+ File::fprintf (f, "%g,\n", lowpass (n, m, wc) * kaiser (n, m, beta));
+ File::close (f);
+}
+
+real β (real A)
+{
+ if (A > 50)
+ return 0.1102 * (A - 8.7);
+ else if (A >= 21)
+ return 0.5842 * (A - 21) ** 0.4 + 0.07886 * (A - 21);
+ else
+ return 0.0;
+}
+
+int M (real A, real Δω)
+{
+ if (A > 21)
+ return ceil ((A - 7.95) / (2.285 * Δω));
+ else
+ return ceil(5.79 / Δω);
+}
+
+typedef struct {
+ real ωpass;
+ real Δω;
+ real A;
+ real β;
+ int M;
+} filter_param_t;
+
+filter_param_t filter (real ωpass, real ωstop, real error)
+{
+ filter_param_t p;
+ p.ωpass = ωpass;
+ p.Δω = ωstop - ωpass;
+ p.A = -20 * log10 (error);
+ p.β = β (p.A);
+ p.M = M (p.A, p.Δω);
+ if ((p.M & 1) == 1)
+ p.M++;
+ return p;
+}
+
+real[] low_pass_filter(real ωpass, real ωstop, real error)
+{
+ filter_param_t p = filter(ωpass, ωstop, error);
+
+ return (real[p.M + 1]) {
+ [n] = lowpass(n, p.M, ωpass) * kaiser(n, p.M, p.β)
+ };
+}
+
+
--- /dev/null
+load "kaiser.5c"
+
+real sinc(real x) = x != 0 ? sin(x)/x : 1;
+
+real sum(real[...] x) { real s = 0; for(int i = 0; i < dim(x); i++) s += x[i]; return s; }
+
+real[...] convolve(real[...] d, real[...] e) {
+ real sample(n) = n < 0 ? d[0] : n >= dim(d) ? d[dim(d)-1] : d[n];
+ real w = floor ((dim(e) - 1) / 2);
+ real c(int center) {
+ real v = 0;
+ real s = 0;
+ int start;
+ int end;
+
+ start = center - w;
+ if (start < 0)
+ start = 0;
+ end = center + w;
+ if (end >= dim(d))
+ end = dim(d) - 1;
+ for (int o = start; o <= end; o++) {
+ real e_o = e[o - center + w];
+ real part = d[o] * e_o;
+ v += part;
+ s += e_o;
+ }
+ v /= s;
+ return v;
+ }
+ return (real[dim(d)]) { [n] = c(n) };
+}
+
+real[...] kaiser_filter(real[...] d, int half_width) {
+# real[half_width * 2 + 1] fir = { [n] = sinc(2 * pi * n / (2 * half_width)) };
+ real M = half_width * 2 + 1;
+ real[M] fir = { [n] = kaiser(n+1, M+1, 8) };
+ return convolve(d, fir);
+}
+
+
+real[1024] square = { [n] = 2 * ((n >> 8) & 1) - 1 };
+
+real[] cut = low_pass_filter(π*1/128, π*1/64, 1e-10);
+
+real[dim(square)] filtered_square = convolve(square, cut);
+
+for (int i = 0; i < dim(filtered_square); i++)
+ printf ("%d %g %g\n", i, square[i], filtered_square[i]);
+
+exit(0);
+
+int size = 100;
+real[size] raw = { [n] = n };
+real[size] filtered = kaiser_filter(raw, 8);
+
+for (int i = 0; i < size; i++)
+ printf ("%d %g %g\n", i, raw[i], filtered[i]);
real gaussian(real x) = exp(-(x**2)/2) / sqrt(2 * pi);
-load "/usr/share/nickle/examples/kaiser.5c"
+load "filter.5c"
real[...] convolve(real[...] d, real[...] e) {
real sample(n) = n < 0 ? d[0] : n >= dim(d) ? d[dim(d)-1] : d[n];
}
void readsamples_telem(file in) {
+ telem_record[...] telem;
+
+ setdim(telem, 0);
+
setdim(clock, 0);
setdim(pressure_value, 0);
setdim(accelerometer_value, 0);
accel_total += save[i].accel;
g_base = accel_total // start;
- for (int i = start; i < dim(save); i++) {
- clock[dim(clock)] = save[i].time/100;
- pressure_value[dim(pressure_value)] = save[i].pressure;
- accelerometer_value[dim(accelerometer_value)] = save[i].accel;
- }
-
+ for (int i = start; i < dim(save); i++)
+ telem[dim(telem)] = save[i];
+
while (!File::end(in)) {
- telem_record t = read_telem(in);
- int n = dim(clock);
- real sample_time = t.time / 100 + clock_bias;
- if (n > 0 && sample_time < clock[n-1]) {
- clock_bias += 65536 / 100;
- sample_time += 65536 / 100;
+ int n = dim(telem);
+ telem[n] = read_telem(in);
+ telem[n].time += clock_bias;
+ if (n > 0 && telem[n].time < telem[n-1].time) {
+ clock_bias += 65536;
+ telem[n].time += 65536;
+ }
+ }
+ int clock_start = telem[0].time;
+ int clock_end = telem[dim(telem)-1].time;
+ int samples = clock_end - clock_start;
+
+ int j = 0;
+ for (int i = 0; i < samples; i++) {
+ clock[i] = i / 100;
+ pressure_value[i] = telem[j].pressure;
+ accelerometer_value[i] = telem[j].accel;
+ if (j < dim(telem)-1) {
+ int cur_time = clock_start + i;
+ if (cur_time - telem[j].time > telem[j+1].time - cur_time)
+ j++;
}
- clock[n] = sample_time;
- pressure_value[dim(pressure_value)] = t.pressure;
- accelerometer_value[dim(accelerometer_value)] = t.accel;
}
}
int size = dim(accelerometer_value);
+real[...] do_low_pass(real[] data, real ωpass, real ωstop, real error) {
+ real[*] fir = low_pass_filter (ωpass, ωstop, error);
+ File::fprintf (stderr, "low pass filter is %d long\n", dim(fir));
+ return convolve(data, fir);
+}
+
if (false) {
accelerometer_value = rebase(accelerometer_value, -1, g_base);
int accel_i0_base = average(accelerometer_value, 30);
} else {
real[size] accelerometer = { [n] = gravity * (count_to_g(accelerometer_value[n]) - 1.0) };
real[size] barometer = { [n] = pressure_to_altitude(count_to_kPa(pressure_value[n] / 16) * 1000) };
- real[size] filtered_accelerometer = kaiser_filter(accelerometer, 8);
- real[size] filtered_barometer = kaiser_filter(barometer, 16);
+ real[size] filtered_accelerometer = do_low_pass(accelerometer,
+ 2 * π * 5/100,
+ 2 * π * 8/100,
+ 1e-8);
+ real[size] filtered_barometer = do_low_pass(barometer,
+ 2 * π * .5 / 100,
+ 2 * π * 1 / 100,
+ 1e-8);
real[...] integrate(real[...] d) {
real[dim(d)] ret;
projects / fw / tmflights / commitdiff