flightgear/src/Instrumentation/altimeter.cxx

// altimeter.cxx - an altimeter tied to the static port.
// Written by David Megginson, started 2002.
//
// This file is in the Public Domain and comes with no warranty.

#include <simgear/math/interpolater.hxx>

#include "altimeter.hxx"
#include <Main/fg_props.hxx>
#include <Main/util.hxx>


// Altitude based on pressure difference from sea level.
// pressure difference inHG, altitude ft
static double altitude_data[][2] = {
 { -8.41, -8858.27 },
 { 0.00, 0.00 },
 { 3.05, 2952.76 },
 { 5.86, 5905.51 },
 { 8.41, 8858.27 },
 { 10.74, 11811.02 },
 { 12.87, 14763.78 },
 { 14.78, 17716.54 },
 { 16.55, 20669.29 },
 { 18.13, 23622.05 },
 { 19.62, 26574.80 },
 { 20.82, 29527.56 },
 { 21.96, 32480.31 },
 { 23.01, 35433.07 },
 { 23.91, 38385.83 },
 { 24.71, 41338.58 },
 { 25.40, 44291.34 },
 { 26.00, 47244.09 },
 { 26.51, 50196.85 },
 { 26.96, 53149.61 },
 { 27.35, 56102.36 },
 { 27.68, 59055.12 },
 { 27.98, 62007.87 },
 { 29.62, 100000.00 },            // just to fill it in
 { -1, -1 }
};


Altimeter::Altimeter ()
    : _altitude_table(new SGInterpTable)
{

    for (int i = 0; altitude_data[i][0] != -1; i++)
        _altitude_table->addEntry(altitude_data[i][0], altitude_data[i][1]);
}

Altimeter::~Altimeter ()
{
    delete _altitude_table;
}

void
Altimeter::init ()
{
    _serviceable_node =
        fgGetNode("/instrumentation/altimeter/serviceable", true);
    _setting_node =
        fgGetNode("/instrumentation/altimeter/setting-inhg", true);
    _pressure_node =
        fgGetNode("/systems/static/pressure-inhg", true);
    _altitude_node =
        fgGetNode("/instrumentation/altimeter/indicated-altitude-ft", true);
}

void
Altimeter::update (double dt)
{
    if (_serviceable_node->getBoolValue()) {
        double pressure = _pressure_node->getDoubleValue();
        double setting = _setting_node->getDoubleValue();
        double altitude =
            fgGetLowPass(_altitude_node->getDoubleValue(),
                         _altitude_table->interpolate(setting - pressure),
                         dt * 10);
        _altitude_node->setDoubleValue(altitude);
    }
}

// end of altimeter.cxx