/* lapse rate and base altitude for each layer in the atmosphere */
const real[NUMBER_OF_LAYERS] lapse_rate = {
- -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002
+ -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002,
};
const int[NUMBER_OF_LAYERS] base_altitude = {
- 0, 11000, 20000, 32000, 47000, 51000, 71000
+ 0, 11000, 20000, 32000, 47000, 51000, 71000,
};
/* calculate the base temperature and pressure for the atmospheric layer
associated with the inputted altitude */
- for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
+ for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 2 && altitude > base_altitude[layer_number + 1]; layer_number++) {
delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
if (lapse_rate[layer_number] == 0.0) {
exponent = GRAVITATIONAL_ACCELERATION * delta_z
/* calculate the base temperature and pressure for the atmospheric layer
associated with the inputted pressure. */
layer_number = -1;
- do {
+ while (layer_number < NUMBER_OF_LAYERS - 2) {
layer_number++;
base_pressure = next_base_pressure;
base_temperature = next_base_temperature;
next_base_pressure *= pow(base, exponent);
}
next_base_temperature += delta_z * lapse_rate[layer_number];
+ if (pressure >= next_base_pressure)
+ break;
}
- while(layer_number < NUMBER_OF_LAYERS - 1 && pressure < next_base_pressure);
/* calculate the altitude associated with the inputted pressure */
if (lapse_rate[layer_number] == 0.0) {
altitude = base_altitude[layer_number]
+ coefficient * (pow(base, exponent) - 1);
}
-
return altitude;
}
-real feet_to_meters(real feet)
-{
- return feet * (12 * 2.54 / 100);
-}
-
-real meters_to_feet(real meters)
-{
- return meters / (12 * 2.54 / 100);
-}
-
/*
* Values for our MS5607
*
typedef struct {
real m, b;
- int m_i, b_i;
} line_t;
+/*
+ * Linear least-squares fit values in the specified array
+ */
line_t best_fit(real[] values, int first, int last) {
real sum_x = 0, sum_x2 = 0, sum_y = 0, sum_xy = 0;
int n = last - first + 1;
real m, b;
- int m_i, b_i;
for (int i = first; i <= last; i++) {
sum_x += i;
return (line_t) { m = m, b = b };
}
-real min_Pa = 0;
-real max_Pa = 120000;
+void print_table (int pa_sample_shift, int pa_part_shift)
+{
+ real min_Pa = 0;
+ real max_Pa = 120000;
-/* Target is an array of < 2000 entries */
-int pa_sample_shift = 3;
-int pa_part_shift = 3;
+ int pa_part_mask = (1 << pa_part_shift) - 1;
-int num_part = ceil(max_Pa / (2 ** (pa_part_shift + pa_sample_shift)));
+ int num_part = ceil(max_Pa / (2 ** (pa_part_shift + pa_sample_shift)));
-int num_samples = num_part << pa_part_shift;
+ int num_samples = num_part << pa_part_shift;
-real sample_to_Pa(int sample) = sample << pa_sample_shift;
+ real sample_to_Pa(int sample) = sample << pa_sample_shift;
-real sample_to_altitude(int sample) = pressure_to_altitude(sample_to_Pa(sample));
+ real sample_to_altitude(int sample) = pressure_to_altitude(sample_to_Pa(sample));
-int part_to_sample(int part) = part << pa_part_shift;
+ int part_to_sample(int part) = part << pa_part_shift;
-real[num_samples] alt = { [n] = sample_to_altitude(n) };
+ int sample_to_part(int sample) = sample >> pa_part_shift;
-int seg_len = 1 << pa_part_shift;
+ bool is_part(int sample) = (sample & pa_part_mask) == 0;
-line_t [num_part] fit = {
- [n] = best_fit(alt, n * seg_len, n * seg_len + seg_len - 1)
-};
+ real[num_samples] alt = { [n] = sample_to_altitude(n) };
-int[num_samples/seg_len + 1] alt_part;
+ int seg_len = 1 << pa_part_shift;
-alt_part[0] = floor (fit[0].b + 0.5);
-alt_part[dim(fit)] = floor(fit[dim(fit)-1].m * dim(fit) * seg_len + fit[dim(fit)-1].b + 0.5);
+ line_t [num_part] fit = {
+ [n] = best_fit(alt, n * seg_len, n * seg_len + seg_len - 1)
+ };
-for (int i = 0; i < dim(fit) - 1; i++) {
- real here, there;
- here = fit[i].m * (i+1) * seg_len + fit[i].b;
- there = fit[i+1].m * (i+1) * seg_len + fit[i+1].b;
- alt_part[i+1] = floor ((here + there) / 2 + 0.5);
-}
+ real[num_samples/seg_len + 1] alt_part;
+ real[dim(alt_part)] alt_error = {0...};
-real sample_to_fit_altitude(int sample) {
- int sub = sample // seg_len;
- int off = sample % seg_len;
- line_t l = fit[sub];
- real r_v;
- real i_v;
+ alt_part[0] = fit[0].b;
+ alt_part[dim(fit)] = fit[dim(fit)-1].m * dim(fit) * seg_len + fit[dim(fit)-1].b;
- r_v = sample * l.m + l.b;
- i_v = (alt_part[sub] * (seg_len - off) + alt_part[sub+1] * off) / seg_len;
- return i_v;
-}
+ for (int i = 0; i < dim(fit) - 1; i++) {
+ real here, there;
+ here = fit[i].m * (i+1) * seg_len + fit[i].b;
+ there = fit[i+1].m * (i+1) * seg_len + fit[i+1].b;
+# printf ("at %d mis-fit %8.2f\n", i, there - here);
+ alt_part[i+1] = (here + there) / 2;
+ }
-real max_error = 0;
-int max_error_sample = 0;
-real total_error = 0;
+ real round(real x) = floor(x + 0.5);
-for (int sample = 0; sample < num_samples; sample++) {
- real Pa = sample_to_Pa(sample);
- real meters = pressure_to_altitude(Pa);
+ real sample_to_fit_altitude(int sample) {
+ int sub = sample // seg_len;
+ int off = sample % seg_len;
+ line_t l = fit[sub];
+ real r_v;
+ real i_v;
- real meters_approx = sample_to_fit_altitude(sample);
- real error = abs(meters - meters_approx);
+ r_v = sample * l.m + l.b;
+ i_v = (round(alt_part[sub]*10) * (seg_len - off) + round(alt_part[sub+1]*10) * off) / seg_len;
+ return i_v/10;
+ }
- total_error += error;
- if (error > max_error) {
- max_error = error;
- max_error_sample = sample;
+ real max_error = 0;
+ int max_error_sample = 0;
+ real total_error = 0;
+
+ for (int sample = 0; sample < num_samples; sample++) {
+ real Pa = sample_to_Pa(sample);
+ real meters = alt[sample];
+
+ real meters_approx = sample_to_fit_altitude(sample);
+ real error = abs(meters - meters_approx);
+
+ int part = sample_to_part(sample);
+
+ if (error > alt_error[part])
+ alt_error[part] = error;
+
+ total_error += error;
+ if (error > max_error) {
+ max_error = error;
+ max_error_sample = sample;
+ }
+ if (false) {
+ printf (" %8.1f %8.2f %8.2f %8.2f %s\n",
+ Pa,
+ meters,
+ meters_approx,
+ meters - meters_approx,
+ is_part(sample) ? "*" : "");
+ }
}
-# printf (" %7d, /* %6.2f kPa %5d sample approx %d */\n",
-# floor (meters + 0.5), Pa / 1000, sample, floor(sample_to_fit_altitude(sample) + 0.5));
-}
-printf ("/*max error %f at %7.3f%%. Average error %f*/\n", max_error, max_error_sample / (num_samples - 1) * 100, total_error / num_samples);
+ printf ("/*max error %f at %7.3f kPa. Average error %f*/\n",
+ max_error, sample_to_Pa(max_error_sample) / 1000, total_error / num_samples);
-printf ("#define NALT %d\n", dim(alt_part));
-printf ("#define ALT_SHIFT %d\n", pa_part_shift + pa_sample_shift);
+ printf ("#define NALT %d\n", dim(alt_part));
+ printf ("#define ALT_SHIFT %d\n", pa_part_shift + pa_sample_shift);
+ printf ("#ifndef AO_ALT_VALUE\n#define AO_ALT_VALUE(x) (alt_t) (x)\n#endif\n");
-for (int part = 0; part < dim(alt_part); part++) {
- real kPa = sample_to_Pa(part_to_sample(part)) / 1000;
- printf ("%9d, /* %6.2f kPa */\n",
- alt_part[part], kPa);
+ for (int part = 0; part < dim(alt_part); part++) {
+ real kPa = sample_to_Pa(part_to_sample(part)) / 1000;
+ printf ("AO_ALT_VALUE(%10.1f), /* %6.2f kPa error %6.2fm */\n",
+ round (alt_part[part]*10) / 10, kPa,
+ alt_error[part]);
+ }
}
+
+autoload ParseArgs;
+
+void main()
+{
+ /* Target is an array of < 1000 entries */
+ int pa_sample_shift = 2;
+ int pa_part_shift = 6;
+
+ ParseArgs::argdesc argd = {
+ .args = {
+ { .var = { .arg_int = &pa_sample_shift },
+ .abbr = 's',
+ .name = "sample",
+ .expr_name = "sample_shift",
+ .desc = "sample shift value" },
+ { .var = { .arg_int = &pa_part_shift },
+ .abbr = 'p',
+ .name = "part",
+ .expr_name = "part_shift",
+ .desc = "part shift value" },
+ }
+ };
+
+ ParseArgs::parseargs(&argd, &argv);
+
+ print_table(pa_sample_shift, pa_part_shift);
+}
+
+main();