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Diffstat (limited to 'altosui/AltosConvert.java')
| -rw-r--r-- | altosui/AltosConvert.java | 192 |
1 files changed, 192 insertions, 0 deletions
diff --git a/altosui/AltosConvert.java b/altosui/AltosConvert.java new file mode 100644 index 00000000..8cc1df27 --- /dev/null +++ b/altosui/AltosConvert.java @@ -0,0 +1,192 @@ +/* + * Copyright © 2010 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. + */ + +/* + * Sensor data conversion functions + */ +package altosui; + +public class AltosConvert { + /* + * 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). + */ + + static final double GRAVITATIONAL_ACCELERATION = -9.80665; + static final double AIR_GAS_CONSTANT = 287.053; + static final double NUMBER_OF_LAYERS = 7; + static final double MAXIMUM_ALTITUDE = 84852.0; + static final double MINIMUM_PRESSURE = 0.3734; + static final double LAYER0_BASE_TEMPERATURE = 288.15; + static final double LAYER0_BASE_PRESSURE = 101325; + + /* lapse rate and base altitude for each layer in the atmosphere */ + static final double[] lapse_rate = { + -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002 + }; + + static final int[] 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 + */ + static double + 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 */ + double 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 *= Math.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 *= Math.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 * Math.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 * Math.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 */ + static double + 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 *= Math.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 *= Math.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 * Math.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 * (Math.pow(base, exponent) - 1); + } + + return altitude; + } + + static double + cc_battery_to_voltage(double battery) + { + return battery / 32767.0 * 5.0; + } + + static double + cc_ignitor_to_voltage(double ignite) + { + return ignite / 32767 * 15.0; + } +} |