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   1 /*
   2  * Copyright © 2010 Keith Packard <keithp@keithp.com>
   3  *
   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.
   7  *
   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.
  12  *
  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.
  16  */
  17
  18 /*
  19  * Sensor data conversion functions
  20  */
  21 package altosui;
  22
  23 public class AltosConvert {
  24         /*
  25          * Pressure Sensor Model, version 1.1
  26          *
  27          * written by Holly Grimes
  28          *
  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.
  33          *
  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
  36          *
  37          * Height measurements use the local tangent plane.  The postive z-direction is up.
  38          *
  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).
  42          */
  43
  44         static final double GRAVITATIONAL_ACCELERATION = -9.80665;
  45         static final double AIR_GAS_CONSTANT            = 287.053;
  46         static final double NUMBER_OF_LAYERS            = 7;
  47         static final double MAXIMUM_ALTITUDE            = 84852.0;
  48         static final double MINIMUM_PRESSURE            = 0.3734;
  49         static final double LAYER0_BASE_TEMPERATURE     = 288.15;
  50         static final double LAYER0_BASE_PRESSURE        = 101325;
  51
  52         /* lapse rate and base altitude for each layer in the atmosphere */
  53         static final double[] lapse_rate = {
  54                 -0.0065, 0.0, 0.001, 0.0028, 0.0, -0.0028, -0.002
  55         };
  56
  57         static final int[] base_altitude = {
  58                 0, 11000, 20000, 32000, 47000, 51000, 71000
  59         };
  60
  61         /* outputs atmospheric pressure associated with the given altitude.
  62          * altitudes are measured with respect to the mean sea level
  63          */
  64         static double
  65         altitude_to_pressure(double altitude)
  66         {
  67                 double base_temperature = LAYER0_BASE_TEMPERATURE;
  68                 double base_pressure = LAYER0_BASE_PRESSURE;
  69
  70                 double 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 */
  75
  76                 if (altitude > MAXIMUM_ALTITUDE) /* FIX ME: use sensor data to improve model */
  77                         return 0;
  78
  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);
  87                         }
  88                         else {
  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);
  93                         }
  94                         base_temperature += delta_z * lapse_rate[layer_number];
  95                 }
  96
  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);
 103                 }
 104                 else {
 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);
 109                 }
 110
 111                 return pressure;
 112         }
 113
 114
 115 /* outputs the altitude associated with the given pressure. the altitude
 116    returned is measured with respect to the mean sea level */
 117         static double
 118         pressure_to_altitude(double pressure)
 119         {
 120
 121                 double next_base_temperature = LAYER0_BASE_TEMPERATURE;
 122                 double next_base_pressure = LAYER0_BASE_PRESSURE;
 123
 124                 double altitude;
 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
 129                                     of next layer */
 130                 double coefficient;
 131                 int layer_number; /* identifies layer in the atmosphere */
 132                 int delta_z; /* difference between two altitudes */
 133
 134                 if (pressure < 0)  /* illegal pressure */
 135                         return -1;
 136                 if (pressure < MINIMUM_PRESSURE) /* FIX ME: use sensor data to improve model */
 137                         return MAXIMUM_ALTITUDE;
 138
 139                 /* calculate the base temperature and pressure for the atmospheric layer
 140                    associated with the inputted pressure. */
 141                 layer_number = -1;
 142                 do {
 143                         layer_number++;
 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);
 151                         }
 152                         else {
 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);
 157                         }
 158                         next_base_temperature += delta_z * lapse_rate[layer_number];
 159                 }
 160                 while(layer_number < NUMBER_OF_LAYERS - 1 && pressure < next_base_pressure);
 161
 162                 /* calculate the altitude associated with the inputted pressure */
 163                 if (lapse_rate[layer_number] == 0.0) {
 164                         coefficient = (AIR_GAS_CONSTANT / GRAVITATIONAL_ACCELERATION)
 165                                 * base_temperature;
 166                         altitude = base_altitude[layer_number]
 167                                 + coefficient * Math.log(pressure / base_pressure);
 168                 }
 169                 else {
 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);
 176                 }
 177
 178                 return altitude;
 179         }
 180
 181         static double
 182         cc_battery_to_voltage(double battery)
 183         {
 184                 return battery / 32767.0 * 5.0;
 185         }
 186
 187         static double
 188         cc_ignitor_to_voltage(double ignite)
 189         {
 190                 return ignite / 32767 * 15.0;
 191         }
 192
 193         static double
 194         radio_setting_to_frequency(int setting, int cal) {
 195                 double  f;
 196
 197                 f = 434.550 * setting / cal;
 198                 /* Round to nearest 50KHz */
 199                 f = Math.floor (20.0 * f + 0.5) / 20.0;
 200                 return f;
 201         }
 202
 203         static int
 204         radio_frequency_to_setting(double frequency, int cal) {
 205                 double  set = frequency / 434.550 * cal;
 206
 207                 return (int) Math.floor (set + 0.5);
 208         }
 209
 210         static double
 211         radio_channel_to_frequency(int channel) {
 212                 return 434.550 + channel * 0.100;
 213         }
 214
 215         static int
 216         radio_frequency_to_channel(double frequency) {
 217                 int     channel = (int) Math.floor ((frequency - 434.550) / 0.100 + 0.5);
 218
 219                 if (channel < 0)
 220                         channel = 0;
 221                 if (channel > 9)
 222                         channel = 9;
 223                 return channel;
 224         }
 225 }