2 * Copyright © 2010 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.
19 * Sensor data conversion functions
21 package org.altusmetrum.AltosLib;
23 public class AltosConvert {
25 * Pressure Sensor Model, version 1.1
27 * written by Holly Grimes
29 * Uses the International Standard Atmosphere as described in
30 * "A Quick Derivation relating altitude to air pressure" (version 1.03)
31 * from the Portland State Aerospace Society, except that the atmosphere
32 * is divided into layers with each layer having a different lapse rate.
34 * Lapse rate data for each layer was obtained from Wikipedia on Sept. 1, 2007
35 * at site <http://en.wikipedia.org/wiki/International_Standard_Atmosphere
37 * Height measurements use the local tangent plane. The postive z-direction is up.
39 * All measurements are given in SI units (Kelvin, Pascal, meter, meters/second^2).
40 * The lapse rate is given in Kelvin/meter, the gas constant for air is given
41 * in Joules/(kilogram-Kelvin).
44 public static final double GRAVITATIONAL_ACCELERATION = -9.80665;
45 public static final double AIR_GAS_CONSTANT = 287.053;
46 public static final double NUMBER_OF_LAYERS = 7;
47 public static final double MAXIMUM_ALTITUDE = 84852.0;
48 public static final double MINIMUM_PRESSURE = 0.3734;
49 public static final double LAYER0_BASE_TEMPERATURE = 288.15;
50 public static final double LAYER0_BASE_PRESSURE = 101325;
52 /* lapse rate and base altitude for each layer in the atmosphere */
53 public static final double[] lapse_rate = {
54 -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002
57 public static final int[] base_altitude = {
58 0, 11000, 20000, 32000, 47000, 51000, 71000
61 /* outputs atmospheric pressure associated with the given altitude.
62 * altitudes are measured with respect to the mean sea level
65 altitude_to_pressure(double altitude)
67 double base_temperature = LAYER0_BASE_TEMPERATURE;
68 double base_pressure = LAYER0_BASE_PRESSURE;
71 double base; /* base for function to determine pressure */
72 double exponent; /* exponent for function to determine pressure */
73 int layer_number; /* identifies layer in the atmosphere */
74 double delta_z; /* difference between two altitudes */
76 if (altitude > MAXIMUM_ALTITUDE) /* FIX ME: use sensor data to improve model */
79 /* calculate the base temperature and pressure for the atmospheric layer
80 associated with the inputted altitude */
81 for(layer_number = 0; layer_number < NUMBER_OF_LAYERS - 1 && altitude > base_altitude[layer_number + 1]; layer_number++) {
82 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
83 if (lapse_rate[layer_number] == 0.0) {
84 exponent = GRAVITATIONAL_ACCELERATION * delta_z
85 / AIR_GAS_CONSTANT / base_temperature;
86 base_pressure *= Math.exp(exponent);
89 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
90 exponent = GRAVITATIONAL_ACCELERATION /
91 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
92 base_pressure *= Math.pow(base, exponent);
94 base_temperature += delta_z * lapse_rate[layer_number];
97 /* calculate the pressure at the inputted altitude */
98 delta_z = altitude - base_altitude[layer_number];
99 if (lapse_rate[layer_number] == 0.0) {
100 exponent = GRAVITATIONAL_ACCELERATION * delta_z
101 / AIR_GAS_CONSTANT / base_temperature;
102 pressure = base_pressure * Math.exp(exponent);
105 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
106 exponent = GRAVITATIONAL_ACCELERATION /
107 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
108 pressure = base_pressure * Math.pow(base, exponent);
115 /* outputs the altitude associated with the given pressure. the altitude
116 returned is measured with respect to the mean sea level */
118 pressure_to_altitude(double pressure)
121 double next_base_temperature = LAYER0_BASE_TEMPERATURE;
122 double next_base_pressure = LAYER0_BASE_PRESSURE;
125 double base_pressure;
126 double base_temperature;
127 double base; /* base for function to determine base pressure of next layer */
128 double exponent; /* exponent for function to determine base pressure
131 int layer_number; /* identifies layer in the atmosphere */
132 int delta_z; /* difference between two altitudes */
134 if (pressure < 0) /* illegal pressure */
136 if (pressure < MINIMUM_PRESSURE) /* FIX ME: use sensor data to improve model */
137 return MAXIMUM_ALTITUDE;
139 /* calculate the base temperature and pressure for the atmospheric layer
140 associated with the inputted pressure. */
144 base_pressure = next_base_pressure;
145 base_temperature = next_base_temperature;
146 delta_z = base_altitude[layer_number + 1] - base_altitude[layer_number];
147 if (lapse_rate[layer_number] == 0.0) {
148 exponent = GRAVITATIONAL_ACCELERATION * delta_z
149 / AIR_GAS_CONSTANT / base_temperature;
150 next_base_pressure *= Math.exp(exponent);
153 base = (lapse_rate[layer_number] * delta_z / base_temperature) + 1.0;
154 exponent = GRAVITATIONAL_ACCELERATION /
155 (AIR_GAS_CONSTANT * lapse_rate[layer_number]);
156 next_base_pressure *= Math.pow(base, exponent);
158 next_base_temperature += delta_z * lapse_rate[layer_number];
160 while(layer_number < NUMBER_OF_LAYERS - 1 && pressure < next_base_pressure);
162 /* calculate the altitude associated with the inputted pressure */
163 if (lapse_rate[layer_number] == 0.0) {
164 coefficient = (AIR_GAS_CONSTANT / GRAVITATIONAL_ACCELERATION)
166 altitude = base_altitude[layer_number]
167 + coefficient * Math.log(pressure / base_pressure);
170 base = pressure / base_pressure;
171 exponent = AIR_GAS_CONSTANT * lapse_rate[layer_number]
172 / GRAVITATIONAL_ACCELERATION;
173 coefficient = base_temperature / lapse_rate[layer_number];
174 altitude = base_altitude[layer_number]
175 + coefficient * (Math.pow(base, exponent) - 1);
182 cc_battery_to_voltage(double battery)
184 return battery / 32767.0 * 5.0;
188 cc_ignitor_to_voltage(double ignite)
190 return ignite / 32767 * 15.0;
193 public static double radio_to_frequency(int freq, int setting, int cal, int channel) {
201 f = 434.550 * setting / cal;
202 /* Round to nearest 50KHz */
203 f = Math.floor (20.0 * f + 0.5) / 20.0;
205 return f + channel * 0.100;
208 public static int radio_frequency_to_setting(double frequency, int cal) {
209 double set = frequency / 434.550 * cal;
211 return (int) Math.floor (set + 0.5);
214 public static int radio_frequency_to_channel(double frequency) {
215 int channel = (int) Math.floor ((frequency - 434.550) / 0.100 + 0.5);
224 public static double radio_channel_to_frequency(int channel) {
225 return 434.550 + channel * 0.100;
228 public static int[] ParseHex(String line) {
229 String[] tokens = line.split("\\s+");
230 int[] array = new int[tokens.length];
232 for (int i = 0; i < tokens.length; i++)
234 array[i] = Integer.parseInt(tokens[i], 16);
235 } catch (NumberFormatException ne) {
241 public static double meters_to_feet(double meters) {
242 return meters * (100 / (2.54 * 12));
245 public static double meters_to_mach(double meters) {
246 return meters / 343; /* something close to mach at usual rocket sites */
249 public static double meters_to_g(double meters) {
250 return meters / 9.80665;
253 public static int checksum(int[] data, int start, int length) {
255 for (int i = 0; i < length; i++)
256 csum += data[i + start];