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; version 2 of the License.
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 * General Public License for more details.
13 * You should have received a copy of the GNU General Public License along
14 * with this program; if not, write to the Free Software Foundation, Inc.,
15 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
22 * Pressure Sensor Model, version 1.1
24 * written by Holly Grimes
26 * Uses the International Standard Atmosphere as described in
27 * "A Quick Derivation relating altitude to air pressure" (version 1.03)
28 * from the Portland State Aerospace Society, except that the atmosphere
29 * is divided into layers with each layer having a different lapse rate.
31 * Lapse rate data for each layer was obtained from Wikipedia on Sept. 1, 2007
32 * at site <http://en.wikipedia.org/wiki/International_Standard_Atmosphere
34 * Height measurements use the local tangent plane. The postive z-direction is up.
36 * All measurements are given in SI units (Kelvin, Pascal, meter, meters/second^2).
37 * The lapse rate is given in Kelvin/meter, the gas constant for air is given
38 * in Joules/(kilogram-Kelvin).
41 #define GRAVITATIONAL_ACCELERATION -9.80665
42 #define AIR_GAS_CONSTANT 287.053
43 #define NUMBER_OF_LAYERS 7
44 #define MAXIMUM_ALTITUDE 84852.0
45 #define MINIMUM_PRESSURE 0.3734
46 #define LAYER0_BASE_TEMPERATURE 288.15
47 #define LAYER0_BASE_PRESSURE 101325
49 /* lapse rate and base altitude for each layer in the atmosphere */
50 static const double lapse_rate[NUMBER_OF_LAYERS] = {
51 -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002
54 static const int base_altitude[NUMBER_OF_LAYERS] = {
55 0, 11000, 20000, 32000, 47000, 51000, 71000
58 /* outputs atmospheric pressure associated with the given altitude. altitudes
59 are measured with respect to the mean sea level */
61 cc_altitude_to_pressure(double altitude)
64 double base_temperature = LAYER0_BASE_TEMPERATURE;
65 double base_pressure = LAYER0_BASE_PRESSURE;
68 double base; /* base for function to determine pressure */
69 double exponent; /* exponent for function to determine pressure */
70 int layer_number; /* identifies layer in the atmosphere */
71 int delta_z; /* difference between two altitudes */
73 if (altitude > MAXIMUM_ALTITUDE) /* FIX ME: use sensor data to improve model */
76 /* calculate the base temperature and pressure for the atmospheric layer
77 associated with the inputted altitude */
78 for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
79 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
80 if (lapse_rate[layer_number] == 0.0) {
81 exponent = GRAVITATIONAL_ACCELERATION * delta_z
82 / AIR_GAS_CONSTANT / base_temperature;
83 base_pressure *= exp(exponent);
86 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
87 exponent = GRAVITATIONAL_ACCELERATION /
88 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
89 base_pressure *= pow(base, exponent);
91 base_temperature += delta_z * lapse_rate[layer_number];
94 /* calculate the pressure at the inputted altitude */
95 delta_z = altitude - base_altitude[layer_number];
96 if (lapse_rate[layer_number] == 0.0) {
97 exponent = GRAVITATIONAL_ACCELERATION * delta_z
98 / AIR_GAS_CONSTANT / base_temperature;
99 pressure = base_pressure * exp(exponent);
102 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
103 exponent = GRAVITATIONAL_ACCELERATION /
104 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
105 pressure = base_pressure * pow(base, exponent);
112 cc_altitude_to_temperature(double altitude)
115 double base_temperature = LAYER0_BASE_TEMPERATURE;
118 int layer_number; /* identifies layer in the atmosphere */
119 double delta_z; /* difference between two altitudes */
121 /* calculate the base temperature for the atmospheric layer
122 associated with the inputted altitude */
123 for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
124 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
125 base_temperature += delta_z * lapse_rate[layer_number];
128 /* calculate the pressure at the inputted altitude */
129 delta_z = altitude - base_altitude[layer_number];
130 temperature = base_temperature + lapse_rate[layer_number] * delta_z;
132 return temperature - 273.15;
135 /* outputs the altitude associated with the given pressure. the altitude
136 returned is measured with respect to the mean sea level */
138 cc_pressure_to_altitude(double pressure)
141 double next_base_temperature = LAYER0_BASE_TEMPERATURE;
142 double next_base_pressure = LAYER0_BASE_PRESSURE;
145 double base_pressure;
146 double base_temperature;
147 double base; /* base for function to determine base pressure of next layer */
148 double exponent; /* exponent for function to determine base pressure
151 int layer_number; /* identifies layer in the atmosphere */
152 int delta_z; /* difference between two altitudes */
154 if (pressure < 0) /* illegal pressure */
156 if (pressure < MINIMUM_PRESSURE) /* FIX ME: use sensor data to improve model */
157 return MAXIMUM_ALTITUDE;
159 /* calculate the base temperature and pressure for the atmospheric layer
160 associated with the inputted pressure. */
164 base_pressure = next_base_pressure;
165 base_temperature = next_base_temperature;
166 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
167 if (lapse_rate[layer_number] == 0.0) {
168 exponent = GRAVITATIONAL_ACCELERATION * delta_z
169 / AIR_GAS_CONSTANT / base_temperature;
170 next_base_pressure *= exp(exponent);
173 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
174 exponent = GRAVITATIONAL_ACCELERATION /
175 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
176 next_base_pressure *= pow(base, exponent);
178 next_base_temperature += delta_z * lapse_rate[layer_number];
180 while(layer_number < NUMBER_OF_LAYERS - 1 && pressure < next_base_pressure);
182 /* calculate the altitude associated with the inputted pressure */
183 if (lapse_rate[layer_number] == 0.0) {
184 coefficient = (AIR_GAS_CONSTANT / GRAVITATIONAL_ACCELERATION)
186 altitude = base_altitude[layer_number]
187 + coefficient * log(pressure / base_pressure);
190 base = pressure / base_pressure;
191 exponent = AIR_GAS_CONSTANT * lapse_rate[layer_number]
192 / GRAVITATIONAL_ACCELERATION;
193 coefficient = base_temperature / lapse_rate[layer_number];
194 altitude = base_altitude[layer_number]
195 + coefficient * (pow(base, exponent) - 1);
202 * Values for our MP3H6115A pressure sensor
204 * From the data sheet:
206 * Pressure range: 15-115 kPa
207 * Voltage at 115kPa: 2.82
208 * Output scale: 27mV/kPa
211 * 27 mV/kPa * 2047 / 3300 counts/mV = 16.75 counts/kPa
212 * 2.82V * 2047 / 3.3 counts/V = 1749 counts/115 kPa
215 static const double counts_per_kPa = 27 * 2047 / 3300;
216 static const double counts_at_101_3kPa = 1674.0;
219 cc_barometer_to_pressure(double count)
221 return ((count / 16.0) / 2047.0 + 0.095) / 0.009 * 1000.0;
225 cc_barometer_to_altitude(double baro)
227 double Pa = cc_barometer_to_pressure(baro);
228 return cc_pressure_to_altitude(Pa);
231 static const double count_per_mss = 27.0;
234 cc_accelerometer_to_acceleration(double accel, double ground_accel)
236 return (ground_accel - accel) / count_per_mss;
239 /* Value for the CC1111 built-in temperature sensor
240 * Output voltage at 0°C = 0.755V
241 * Coefficient = 0.00247V/°C
242 * Reference voltage = 1.25V
244 * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
245 * = (value - 19791.268) / 32768 * 1.25 / 0.00247
249 cc_thermometer_to_temperature(double thermo)
251 return (thermo - 19791.268) / 32728.0 * 1.25 / 0.00247;
255 cc_battery_to_voltage(double battery)
257 return battery / 32767.0 * 5.0;
261 cc_ignitor_to_voltage(double ignite)
263 return ignite / 32767 * 15.0;
266 static inline double sqr(double a) { return a * a; }
269 cc_great_circle (double start_lat, double start_lon,
270 double end_lat, double end_lon,
271 double *dist, double *bearing)
273 const double rad = M_PI / 180;
274 const double earth_radius = 6371.2 * 1000; /* in meters */
275 double lat1 = rad * start_lat;
276 double lon1 = rad * -start_lon;
277 double lat2 = rad * end_lat;
278 double lon2 = rad * -end_lon;
280 // double d_lat = lat2 - lat1;
281 double d_lon = lon2 - lon1;
283 /* From http://en.wikipedia.org/wiki/Great-circle_distance */
284 double vdn = sqrt(sqr(cos(lat2) * sin(d_lon)) +
285 sqr(cos(lat1) * sin(lat2) -
286 sin(lat1) * cos(lat2) * cos(d_lon)));
287 double vdd = sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(d_lon);
288 double d = atan2(vdn,vdd);
291 if (cos(lat1) < 1e-20) {
300 course = acos((sin(lat2)-sin(lat1)*cos(d)) /
302 if (sin(lon2-lon1) > 0)
303 course = 2 * M_PI-course;
305 *dist = d * earth_radius;
306 *bearing = course * 180/M_PI;