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Diffstat (limited to 'ao-tools/lib/cc-convert.c')
| -rw-r--r-- | ao-tools/lib/cc-convert.c | 275 |
1 files changed, 275 insertions, 0 deletions
diff --git a/ao-tools/lib/cc-convert.c b/ao-tools/lib/cc-convert.c new file mode 100644 index 00000000..ac6962ba --- /dev/null +++ b/ao-tools/lib/cc-convert.c @@ -0,0 +1,275 @@ +/* + * Copyright © 2009 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 "cc.h" +#include <math.h> + +/* + * 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). + */ + +#define GRAVITATIONAL_ACCELERATION -9.80665 +#define AIR_GAS_CONSTANT 287.053 +#define NUMBER_OF_LAYERS 7 +#define MAXIMUM_ALTITUDE 84852.0 +#define MINIMUM_PRESSURE 0.3734 +#define LAYER0_BASE_TEMPERATURE 288.15 +#define LAYER0_BASE_PRESSURE 101325 + +/* lapse rate and base altitude for each layer in the atmosphere */ +static const double lapse_rate[NUMBER_OF_LAYERS] = { + -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002 +}; + +static const int base_altitude[NUMBER_OF_LAYERS] = { + 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 */ +double +cc_altitude_to_pressure(double altitude) +{ + + double base_temperature = LAYER0_BASE_TEMPERATURE; + double base_pressure = LAYER0_BASE_PRESSURE; + + double pressure; + double base; /* base for function to determine pressure */ + double 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 */ +double +cc_pressure_to_altitude(double pressure) +{ + + double next_base_temperature = LAYER0_BASE_TEMPERATURE; + double next_base_pressure = LAYER0_BASE_PRESSURE; + + double altitude; + double base_pressure; + double base_temperature; + double base; /* base for function to determine base pressure of next layer */ + double exponent; /* exponent for function to determine base pressure + of next layer */ + double 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; +} + +/* + * Values for our MP3H6115A pressure sensor + * + * From the data sheet: + * + * Pressure range: 15-115 kPa + * Voltage at 115kPa: 2.82 + * Output scale: 27mV/kPa + * + * + * 27 mV/kPa * 2047 / 3300 counts/mV = 16.75 counts/kPa + * 2.82V * 2047 / 3.3 counts/V = 1749 counts/115 kPa + */ + +static const double counts_per_kPa = 27 * 2047 / 3300; +static const double counts_at_101_3kPa = 1674.0; + +double +cc_barometer_to_pressure(double count) +{ + return ((count / 16.0) / 2047.0 + 0.095) / 0.009 * 1000.0; +} + +double +cc_barometer_to_altitude(double baro) +{ + double Pa = cc_barometer_to_pressure(baro); + return cc_pressure_to_altitude(Pa); +} + +static const double count_per_mss = 27.0; + +double +cc_accelerometer_to_acceleration(double accel, double ground_accel) +{ + return (ground_accel - accel) / count_per_mss; +} + +double +cc_thermometer_to_temperature(double thermo) +{ + return ((thermo / 32767 * 3.3) - 0.5) / 0.01; +} + +double +cc_battery_to_voltage(double battery) +{ + return battery / 32767.0 * 5.0; +} + +double +cc_ignitor_to_voltage(double ignite) +{ + return ignite / 32767 * 15.0; +} + +static inline double sqr(double a) { return a * a; } + +void +cc_great_circle (double start_lat, double start_lon, + double end_lat, double end_lon, + double *dist, double *bearing) +{ + const double rad = M_PI / 180; + const double earth_radius = 6371.2 * 1000; /* in meters */ + double lat1 = rad * start_lat; + double lon1 = rad * -start_lon; + double lat2 = rad * end_lat; + double lon2 = rad * -end_lon; + +// double d_lat = lat2 - lat1; + double d_lon = lon2 - lon1; + + /* From http://en.wikipedia.org/wiki/Great-circle_distance */ + double vdn = sqrt(sqr(cos(lat2) * sin(d_lon)) + + sqr(cos(lat1) * sin(lat2) - + sin(lat1) * cos(lat2) * cos(d_lon))); + double vdd = sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(d_lon); + double d = atan2(vdn,vdd); + double course; + + if (cos(lat1) < 1e-20) { + if (lat1 > 0) + course = M_PI; + else + course = -M_PI; + } else { + if (d < 1e-10) + course = 0; + else + course = acos((sin(lat2)-sin(lat1)*cos(d)) / + (sin(d)*cos(lat1))); + if (sin(lon2-lon1) > 0) + course = 2 * M_PI-course; + } + *dist = d * earth_radius; + *bearing = course * 180/M_PI; +} |