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-rw-r--r--src/util/make-altitude-pa78
1 files changed, 46 insertions, 32 deletions
diff --git a/src/util/make-altitude-pa b/src/util/make-altitude-pa
index 190b36fc..eae5ebe9 100644
--- a/src/util/make-altitude-pa
+++ b/src/util/make-altitude-pa
@@ -29,10 +29,10 @@ const real LAYER0_BASE_PRESSURE = 101325;
/* 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,
};
@@ -54,7 +54,7 @@ real altitude_to_pressure(real altitude) {
/* 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
@@ -113,7 +113,7 @@ real pressure_to_altitude(real pressure) {
/* 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;
@@ -130,8 +130,9 @@ real pressure_to_altitude(real pressure) {
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) {
@@ -148,20 +149,9 @@ real pressure_to_altitude(real pressure) {
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
*
@@ -174,14 +164,15 @@ real meters_to_feet(real meters)
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;
@@ -197,9 +188,10 @@ line_t best_fit(real[] values, int first, int last) {
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;
+/* Target is an array of < 1000 entries */
+int pa_sample_shift = 2;
+int pa_part_shift = 6;
+int pa_part_mask = (1 << pa_part_shift) - 1;
int num_part = ceil(max_Pa / (2 ** (pa_part_shift + pa_sample_shift)));
@@ -211,6 +203,10 @@ real sample_to_altitude(int sample) = pressure_to_altitude(sample_to_Pa(sample))
int part_to_sample(int part) = part << pa_part_shift;
+int sample_to_part(int sample) = sample >> pa_part_shift;
+
+bool is_part(int sample) = (sample & pa_part_mask) == 0;
+
real[num_samples] alt = { [n] = sample_to_altitude(n) };
int seg_len = 1 << pa_part_shift;
@@ -219,18 +215,22 @@ line_t [num_part] fit = {
[n] = best_fit(alt, n * seg_len, n * seg_len + seg_len - 1)
};
-int[num_samples/seg_len + 1] alt_part;
+real[num_samples/seg_len + 1] alt_part;
+real[dim(alt_part)] alt_error = {0...};
-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);
+alt_part[0] = fit[0].b;
+alt_part[dim(fit)] = fit[dim(fit)-1].m * dim(fit) * seg_len + fit[dim(fit)-1].b;
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);
+# printf ("at %d mis-fit %8.2f\n", i, there - here);
+ alt_part[i+1] = (here + there) / 2;
}
+real round(real x) = floor(x + 0.5);
+
real sample_to_fit_altitude(int sample) {
int sub = sample // seg_len;
int off = sample % seg_len;
@@ -239,7 +239,7 @@ real sample_to_fit_altitude(int sample) {
real i_v;
r_v = sample * l.m + l.b;
- i_v = (alt_part[sub] * (seg_len - off) + alt_part[sub+1] * off) / seg_len;
+ i_v = (round(alt_part[sub]) * (seg_len - off) + round(alt_part[sub+1]) * off) / seg_len;
return i_v;
}
@@ -249,27 +249,41 @@ real total_error = 0;
for (int sample = 0; sample < num_samples; sample++) {
real Pa = sample_to_Pa(sample);
- real meters = pressure_to_altitude(Pa);
+ 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;
}
-# 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));
+ if (false) {
+ printf (" %8.1f %8.2f %8.2f %8.2f %s\n",
+ Pa,
+ meters,
+ meters_approx,
+ meters - meters_approx,
+ is_part(sample) ? "*" : "");
+ }
}
-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 ("#ifndef SATURATE\n#define SATURATE(x) (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);
+ printf ("SATURATE(%9d), /* %6.2f kPa error %6.2fm */\n",
+ round (alt_part[part]), kPa,
+ alt_error[part]);
}
generated by cgit v1.2.3 (git 2.39.1) at 2025-10-31 02:34:40 +0000