--- /dev/null
+/*
+ * 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;
+}
projects / fw / altos / blobdiff