2 * Copyright © 2009 Keith Packard <keithp@keithp.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
23 * Pressure Sensor Model, version 1.1
25 * written by Holly Grimes
27 * Uses the International Standard Atmosphere as described in
28 * "A Quick Derivation relating altitude to air pressure" (version 1.03)
29 * from the Portland State Aerospace Society, except that the atmosphere
30 * is divided into layers with each layer having a different lapse rate.
32 * Lapse rate data for each layer was obtained from Wikipedia on Sept. 1, 2007
33 * at site <http://en.wikipedia.org/wiki/International_Standard_Atmosphere
35 * Height measurements use the local tangent plane. The postive z-direction is up.
37 * All measurements are given in SI units (Kelvin, Pascal, meter, meters/second^2).
38 * The lapse rate is given in Kelvin/meter, the gas constant for air is given
39 * in Joules/(kilogram-Kelvin).
42 #define GRAVITATIONAL_ACCELERATION -9.80665
43 #define AIR_GAS_CONSTANT 287.053
44 #define NUMBER_OF_LAYERS 7
45 #define MAXIMUM_ALTITUDE 84852.0
46 #define MINIMUM_PRESSURE 0.3734
47 #define LAYER0_BASE_TEMPERATURE 288.15
48 #define LAYER0_BASE_PRESSURE 101325
50 /* lapse rate and base altitude for each layer in the atmosphere */
51 static const double lapse_rate[NUMBER_OF_LAYERS] = {
52 -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002
55 static const int base_altitude[NUMBER_OF_LAYERS] = {
56 0, 11000, 20000, 32000, 47000, 51000, 71000
59 /* outputs atmospheric pressure associated with the given altitude. altitudes
60 are measured with respect to the mean sea level */
62 cc_altitude_to_pressure(double altitude)
65 double base_temperature = LAYER0_BASE_TEMPERATURE;
66 double base_pressure = LAYER0_BASE_PRESSURE;
69 double base; /* base for function to determine pressure */
70 double exponent; /* exponent for function to determine pressure */
71 int layer_number; /* identifies layer in the atmosphere */
72 int delta_z; /* difference between two altitudes */
74 if (altitude > MAXIMUM_ALTITUDE) /* FIX ME: use sensor data to improve model */
77 /* calculate the base temperature and pressure for the atmospheric layer
78 associated with the inputted altitude */
79 for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
80 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
81 if (lapse_rate[layer_number] == 0.0) {
82 exponent = GRAVITATIONAL_ACCELERATION * delta_z
83 / AIR_GAS_CONSTANT / base_temperature;
84 base_pressure *= exp(exponent);
87 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
88 exponent = GRAVITATIONAL_ACCELERATION /
89 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
90 base_pressure *= pow(base, exponent);
92 base_temperature += delta_z * lapse_rate[layer_number];
95 /* calculate the pressure at the inputted altitude */
96 delta_z = altitude - base_altitude[layer_number];
97 if (lapse_rate[layer_number] == 0.0) {
98 exponent = GRAVITATIONAL_ACCELERATION * delta_z
99 / AIR_GAS_CONSTANT / base_temperature;
100 pressure = base_pressure * exp(exponent);
103 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
104 exponent = GRAVITATIONAL_ACCELERATION /
105 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
106 pressure = base_pressure * pow(base, exponent);
113 cc_altitude_to_temperature(double altitude)
116 double base_temperature = LAYER0_BASE_TEMPERATURE;
119 int layer_number; /* identifies layer in the atmosphere */
120 double delta_z; /* difference between two altitudes */
122 /* calculate the base temperature for the atmospheric layer
123 associated with the inputted altitude */
124 for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
125 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
126 base_temperature += delta_z * lapse_rate[layer_number];
129 /* calculate the pressure at the inputted altitude */
130 delta_z = altitude - base_altitude[layer_number];
131 temperature = base_temperature + lapse_rate[layer_number] * delta_z;
133 return temperature - 273.15;
136 /* outputs the altitude associated with the given pressure. the altitude
137 returned is measured with respect to the mean sea level */
139 cc_pressure_to_altitude(double pressure)
142 double next_base_temperature = LAYER0_BASE_TEMPERATURE;
143 double next_base_pressure = LAYER0_BASE_PRESSURE;
146 double base_pressure;
147 double base_temperature;
148 double base; /* base for function to determine base pressure of next layer */
149 double exponent; /* exponent for function to determine base pressure
152 int layer_number; /* identifies layer in the atmosphere */
153 int delta_z; /* difference between two altitudes */
155 if (pressure < 0) /* illegal pressure */
157 if (pressure < MINIMUM_PRESSURE) /* FIX ME: use sensor data to improve model */
158 return MAXIMUM_ALTITUDE;
160 /* calculate the base temperature and pressure for the atmospheric layer
161 associated with the inputted pressure. */
165 base_pressure = next_base_pressure;
166 base_temperature = next_base_temperature;
167 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
168 if (lapse_rate[layer_number] == 0.0) {
169 exponent = GRAVITATIONAL_ACCELERATION * delta_z
170 / AIR_GAS_CONSTANT / base_temperature;
171 next_base_pressure *= exp(exponent);
174 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
175 exponent = GRAVITATIONAL_ACCELERATION /
176 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
177 next_base_pressure *= pow(base, exponent);
179 next_base_temperature += delta_z * lapse_rate[layer_number];
181 while(layer_number < NUMBER_OF_LAYERS - 1 && pressure < next_base_pressure);
183 /* calculate the altitude associated with the inputted pressure */
184 if (lapse_rate[layer_number] == 0.0) {
185 coefficient = (AIR_GAS_CONSTANT / GRAVITATIONAL_ACCELERATION)
187 altitude = base_altitude[layer_number]
188 + coefficient * log(pressure / base_pressure);
191 base = pressure / base_pressure;
192 exponent = AIR_GAS_CONSTANT * lapse_rate[layer_number]
193 / GRAVITATIONAL_ACCELERATION;
194 coefficient = base_temperature / lapse_rate[layer_number];
195 altitude = base_altitude[layer_number]
196 + coefficient * (pow(base, exponent) - 1);
203 * Values for our MP3H6115A pressure sensor
205 * From the data sheet:
207 * Pressure range: 15-115 kPa
208 * Voltage at 115kPa: 2.82
209 * Output scale: 27mV/kPa
212 * 27 mV/kPa * 2047 / 3300 counts/mV = 16.75 counts/kPa
213 * 2.82V * 2047 / 3.3 counts/V = 1749 counts/115 kPa
217 cc_barometer_to_pressure(double count)
219 return ((count / 16.0) / 2047.0 + 0.095) / 0.009 * 1000.0;
223 cc_barometer_to_altitude(double baro)
225 double Pa = cc_barometer_to_pressure(baro);
226 return cc_pressure_to_altitude(Pa);
229 static const double count_per_mss = 27.0;
232 cc_accelerometer_to_acceleration(double accel, double ground_accel)
234 return (ground_accel - accel) / count_per_mss;
237 /* Value for the CC1111 built-in temperature sensor
238 * Output voltage at 0°C = 0.755V
239 * Coefficient = 0.00247V/°C
240 * Reference voltage = 1.25V
242 * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
243 * = (value - 19791.268) / 32768 * 1.25 / 0.00247
247 cc_thermometer_to_temperature(double thermo)
249 return (thermo - 19791.268) / 32728.0 * 1.25 / 0.00247;
253 cc_battery_to_voltage(double battery)
255 return battery / 32767.0 * 5.0;
259 cc_ignitor_to_voltage(double ignite)
261 return ignite / 32767 * 15.0;
264 static inline double sqr(double a) { return a * a; }
267 cc_great_circle (double start_lat, double start_lon,
268 double end_lat, double end_lon,
269 double *dist, double *bearing)
271 const double rad = M_PI / 180;
272 const double earth_radius = 6371.2 * 1000; /* in meters */
273 double lat1 = rad * start_lat;
274 double lon1 = rad * -start_lon;
275 double lat2 = rad * end_lat;
276 double lon2 = rad * -end_lon;
278 // double d_lat = lat2 - lat1;
279 double d_lon = lon2 - lon1;
281 /* From http://en.wikipedia.org/wiki/Great-circle_distance */
282 double vdn = sqrt(sqr(cos(lat2) * sin(d_lon)) +
283 sqr(cos(lat1) * sin(lat2) -
284 sin(lat1) * cos(lat2) * cos(d_lon)));
285 double vdd = sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(d_lon);
286 double d = atan2(vdn,vdd);
289 if (cos(lat1) < 1e-20) {
298 course = acos((sin(lat2)-sin(lat1)*cos(d)) /
300 if (sin(lon2-lon1) > 0)
301 course = 2 * M_PI-course;
303 *dist = d * earth_radius;
304 *bearing = course * 180/M_PI;