diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/Makefile | 6 | ||||
| -rw-r--r-- | src/core/ao.h | 12 | ||||
| -rw-r--r-- | src/core/ao_convert_pa.c | 72 | ||||
| -rw-r--r-- | src/core/ao_convert_pa_test.c | 76 | ||||
| -rw-r--r-- | src/test/Makefile | 5 | ||||
| -rw-r--r-- | src/util/make-altitude-pa | 275 |
6 files changed, 444 insertions, 2 deletions
diff --git a/src/Makefile b/src/Makefile index db9bd508..c2e324c4 100644 --- a/src/Makefile +++ b/src/Makefile @@ -4,6 +4,7 @@ # vpath make-altitude util +vpath make-altitude-pa util vpath make-kalman util vpath kalman.5c kalman vpath kalman_filter.5c kalman @@ -45,11 +46,14 @@ uninstall: all-recursive: all-local -all-local: altitude.h ao_kalman.h +all-local: altitude.h altitude-pa.h ao_kalman.h altitude.h: make-altitude nickle $< > $@ +altitude-pa.h: make-altitude-pa + nickle $< > $@ + ao_kalman.h: make-kalman kalman.5c kalman_filter.5c load_csv.5c matrix.5c bash $< kalman > $@ diff --git a/src/core/ao.h b/src/core/ao.h index 27b9c5c4..a2092cfe 100644 --- a/src/core/ao.h +++ b/src/core/ao.h @@ -282,6 +282,18 @@ ao_altitude_to_pres(int16_t alt) __reentrant; int16_t ao_temp_to_dC(int16_t temp) __reentrant; +/* + * ao_convert_pa.c + * + * Convert between pressure in Pa and altitude in meters + */ + +int32_t +ao_pa_to_altitude(int32_t pa); + +int32_t +ao_altitude_to_pa(int32_t alt); + #if HAS_DBG #include <ao_dbg.h> #endif diff --git a/src/core/ao_convert_pa.c b/src/core/ao_convert_pa.c new file mode 100644 index 00000000..0c93caea --- /dev/null +++ b/src/core/ao_convert_pa.c @@ -0,0 +1,72 @@ +/* + * Copyright © 2012 Keith Packard <keithp@keithp.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; version 2 of the License. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. + */ + +#if !defined(AO_CONVERT_TEST) && !defined(AO_FLIGHT_TEST) +#include "ao.h" +#endif + +static const int32_t altitude_table[] = { +#include "altitude-pa.h" +}; + +#define ALT_SCALE (1 << ALT_SHIFT) +#define ALT_MASK (ALT_SCALE - 1) + +int32_t +ao_pa_to_altitude(int32_t pa) +{ + int16_t o; + int16_t part; + int32_t low, high; + + if (pa < 0) + pa = 0; + if (pa > 120000) + pa = 120000; + o = pa >> ALT_SHIFT; + part = pa & ALT_MASK; + + low = (int32_t) altitude_table[o] * (ALT_SCALE - part); + high = (int32_t) altitude_table[o+1] * part + (ALT_SCALE >> 1); + return (low + high) >> ALT_SHIFT; +} + +int32_t +ao_altitude_to_pa(int32_t alt) +{ + int32_t span, sub_span; + uint16_t l, h, m; + int32_t pa; + + l = 0; + h = NALT - 1; + while ((h - l) != 1) { + m = (l + h) >> 1; + if (altitude_table[m] < alt) + h = m; + else + l = m; + } + span = altitude_table[l] - altitude_table[h]; + sub_span = altitude_table[l] - alt; + pa = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_SHIFT) + (span >> 1)) / span; + if (pa > 120000) + pa = 120000; + if (pa < 0) + pa = 0; + return pa; +} diff --git a/src/core/ao_convert_pa_test.c b/src/core/ao_convert_pa_test.c new file mode 100644 index 00000000..972a4d4c --- /dev/null +++ b/src/core/ao_convert_pa_test.c @@ -0,0 +1,76 @@ +/* + * Copyright © 2012 Keith Packard <keithp@keithp.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; version 2 of the License. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. + */ + +#include <stdint.h> +#define AO_CONVERT_TEST +#include "ao_host.h" +#include "ao_convert_pa.c" + +#define STEP_P 1 +#define STEP_A 1 + +static inline i_abs(int i) { return i < 0 ? -i : i; } + +main () +{ + int i; + int32_t p_to_a, p_to_a_to_p; + int32_t a_to_p, a_to_p_to_a; + int max_p_error = 0, max_p_error_p = -1; + int max_a_error = 0, max_a_error_a = -1; + int p_error; + int a_error; + int ret = 0; + + for (i = 0; i < 120000 + STEP_P; i += STEP_P) { + if (i > 120000) + i = 120000; + p_to_a = ao_pa_to_altitude(i); + p_to_a_to_p = ao_altitude_to_pa(p_to_a); + p_error = i_abs(p_to_a_to_p - i); + if (p_error > max_p_error) { + max_p_error = p_error; + max_p_error_p = i; + } +// printf ("pa %d alt %d pa %d\n", +// i, p_to_a, p_to_a_to_p); + } + for (i = -1450; i < 74250 + STEP_A; i += STEP_A) { + if (i > 74250) + i = 74250; + a_to_p = ao_altitude_to_pa(i); + a_to_p_to_a = ao_pa_to_altitude(a_to_p); + a_error = i_abs(a_to_p_to_a - i); + if (a_error > max_a_error) { + max_a_error = a_error; + max_a_error_a = i; + } +// printf ("alt %d pa %d alt %d\n", +// i, a_to_p, a_to_p_to_a); + } + if (max_p_error > 2) { + printf ("max p error %d at %d\n", max_p_error, + max_p_error_p); + ret++; + } + if (max_a_error > 1) { + printf ("max a error %d at %d\n", max_a_error, + max_a_error_a); + ret++; + } + return ret; +} diff --git a/src/test/Makefile b/src/test/Makefile index 4e403da6..3c2b8732 100644 --- a/src/test/Makefile +++ b/src/test/Makefile @@ -1,6 +1,6 @@ vpath % ..:../core:../drivers:../util -PROGS=ao_flight_test ao_flight_test_baro ao_flight_test_accel ao_flight_test_noisy_accel ao_gps_test ao_gps_test_skytraq ao_convert_test +PROGS=ao_flight_test ao_flight_test_baro ao_flight_test_accel ao_flight_test_noisy_accel ao_gps_test ao_gps_test_skytraq ao_convert_test ao_convert_pa_test KALMAN=make-kalman @@ -34,5 +34,8 @@ ao_gps_test_skytraq: ao_gps_test_skytraq.c ao_gps_skytraq.c ao_gps_print.c ao_ho ao_convert_test: ao_convert_test.c ao_convert.c altitude.h cc $(CFLAGS) -o $@ $< +ao_convert_pa_test: ao_convert_pa_test.c ao_convert_pa.c altitude-pa.h + cc $(CFLAGS) -o $@ $< + ao_kalman.h: $(KALMAN) (cd .. && make ao_kalman.h)
\ No newline at end of file diff --git a/src/util/make-altitude-pa b/src/util/make-altitude-pa new file mode 100644 index 00000000..190b36fc --- /dev/null +++ b/src/util/make-altitude-pa @@ -0,0 +1,275 @@ +#!/usr/bin/nickle -f +/* + * Pressure Sensor Model, version 1.1 + * + * written by Holly Grimes + * + * Uses the International Standard Atmosphere as described in + * "A Quick Derivation relating altitude to air pressure" (version 1.03) + * from the Portland State Aerospace Society, except that the atmosphere + * is divided into layers with each layer having a different lapse rate. + * + * Lapse rate data for each layer was obtained from Wikipedia on Sept. 1, 2007 + * at site <http://en.wikipedia.org/wiki/International_Standard_Atmosphere + * + * Height measurements use the local tangent plane. The postive z-direction is up. + * + * All measurements are given in SI units (Kelvin, Pascal, meter, meters/second^2). + * The lapse rate is given in Kelvin/meter, the gas constant for air is given + * in Joules/(kilogram-Kelvin). + */ + +const real GRAVITATIONAL_ACCELERATION = -9.80665; +const real AIR_GAS_CONSTANT = 287.053; +const int NUMBER_OF_LAYERS = 7; +const real MAXIMUM_ALTITUDE = 84852; +const real MINIMUM_PRESSURE = 0.3734; +const real LAYER0_BASE_TEMPERATURE = 288.15; +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 +}; +const int[NUMBER_OF_LAYERS] base_altitude = { + 0, 11000, 20000, 32000, 47000, 51000, 71000 +}; + + +/* outputs atmospheric pressure associated with the given altitude. altitudes + are measured with respect to the mean sea level */ +real altitude_to_pressure(real altitude) { + + real base_temperature = LAYER0_BASE_TEMPERATURE; + real base_pressure = LAYER0_BASE_PRESSURE; + + real pressure; + real base; /* base for function to determine pressure */ + real exponent; /* exponent for function to determine pressure */ + int layer_number; /* identifies layer in the atmosphere */ + int delta_z; /* difference between two altitudes */ + + if (altitude > MAXIMUM_ALTITUDE) /* FIX ME: use sensor data to improve model */ + return 0; + + /* 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++) { + delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number]; + if (lapse_rate[layer_number] == 0.0) { + exponent = GRAVITATIONAL_ACCELERATION * delta_z + / AIR_GAS_CONSTANT / base_temperature; + base_pressure *= exp(exponent); + } + else { + base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0; + exponent = GRAVITATIONAL_ACCELERATION / + (AIR_GAS_CONSTANT * lapse_rate[layer_number]); + base_pressure *= pow(base, exponent); + } + base_temperature += delta_z * lapse_rate[layer_number]; + } + + /* calculate the pressure at the inputted altitude */ + delta_z = altitude - base_altitude[layer_number]; + if (lapse_rate[layer_number] == 0.0) { + exponent = GRAVITATIONAL_ACCELERATION * delta_z + / AIR_GAS_CONSTANT / base_temperature; + pressure = base_pressure * exp(exponent); + } + else { + base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0; + exponent = GRAVITATIONAL_ACCELERATION / + (AIR_GAS_CONSTANT * lapse_rate[layer_number]); + pressure = base_pressure * pow(base, exponent); + } + + return pressure; +} + + +/* outputs the altitude associated with the given pressure. the altitude + returned is measured with respect to the mean sea level */ +real pressure_to_altitude(real pressure) { + + real next_base_temperature = LAYER0_BASE_TEMPERATURE; + real next_base_pressure = LAYER0_BASE_PRESSURE; + + real altitude; + real base_pressure; + real base_temperature; + real base; /* base for function to determine base pressure of next layer */ + real exponent; /* exponent for function to determine base pressure + of next layer */ + real coefficient; + int layer_number; /* identifies layer in the atmosphere */ + int delta_z; /* difference between two altitudes */ + + if (pressure < 0) /* illegal pressure */ + return -1; + if (pressure < MINIMUM_PRESSURE) /* FIX ME: use sensor data to improve model */ + return MAXIMUM_ALTITUDE; + + /* calculate the base temperature and pressure for the atmospheric layer + associated with the inputted pressure. */ + layer_number = -1; + do { + layer_number++; + base_pressure = next_base_pressure; + base_temperature = next_base_temperature; + delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number]; + if (lapse_rate[layer_number] == 0.0) { + exponent = GRAVITATIONAL_ACCELERATION * delta_z + / AIR_GAS_CONSTANT / base_temperature; + next_base_pressure *= exp(exponent); + } + else { + base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0; + exponent = GRAVITATIONAL_ACCELERATION / + (AIR_GAS_CONSTANT * lapse_rate[layer_number]); + next_base_pressure *= pow(base, exponent); + } + next_base_temperature += delta_z * lapse_rate[layer_number]; + } + 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) { + coefficient = (AIR_GAS_CONSTANT / GRAVITATIONAL_ACCELERATION) + * base_temperature; + altitude = base_altitude[layer_number] + + coefficient * log(pressure / base_pressure); + } + else { + base = pressure / base_pressure; + exponent = AIR_GAS_CONSTANT * lapse_rate[layer_number] + / GRAVITATIONAL_ACCELERATION; + coefficient = base_temperature / lapse_rate[layer_number]; + 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 + * + * From the data sheet: + * + * Pressure range: 10-1200 mbar (1000 - 120000 Pa) + * + * Pressure data is reported in units of Pa + */ + +typedef struct { + real m, b; + int m_i, b_i; +} line_t; + +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; + sum_x2 += i**2; + sum_y += values[i]; + sum_xy += values[i] * i; + } + m = (n*sum_xy - sum_y*sum_x) / (n*sum_x2 - sum_x**2); + b = sum_y/n - m*(sum_x/n); + return (line_t) { m = m, b = b }; +} + +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 num_part = ceil(max_Pa / (2 ** (pa_part_shift + pa_sample_shift))); + +int num_samples = num_part << pa_part_shift; + +real sample_to_Pa(int sample) = sample << pa_sample_shift; + +real sample_to_altitude(int sample) = pressure_to_altitude(sample_to_Pa(sample)); + +int part_to_sample(int part) = part << pa_part_shift; + +real[num_samples] alt = { [n] = sample_to_altitude(n) }; + +int seg_len = 1 << pa_part_shift; + +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; + +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); + +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 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; + + 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; +} + +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 = pressure_to_altitude(Pa); + + real meters_approx = sample_to_fit_altitude(sample); + real error = abs(meters - meters_approx); + + 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)); +} + +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 ("#define NALT %d\n", dim(alt_part)); +printf ("#define ALT_SHIFT %d\n", pa_part_shift + pa_sample_shift); + +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); +} |