src/Atmosphere/AirDensity.cpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #include "AirDensity.hpp"
  25
  26 #define isa_sea_level_density fixed(1.225)
  27 #define k4 fixed(44330.8)
  28 #define k6 fixed(1.0 / 42266.5)
  29 #define k7 fixed(1.0 / 0.234969)
  30
  31 fixed
  32 AirDensity(const fixed altitude)
  33 {
  34   return fixed(pow((k4 - altitude) * k6, k7));
  35 }
  36
  37 fixed
  38 AirDensityRatio(const fixed altitude)
  39 {
  40   return sqrt(isa_sea_level_density / AirDensity(altitude));
  41 }