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src/Instrumentation/attitude_indicator.cxx

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+// attitude_indicator.cxx - a vacuum-powered attitude indicator.
+// Written by David Megginson, started 2002.
+//
+// This file is in the Public Domain and comes with no warranty.
+
+// TODO:
+// - better spin-up
+
+#ifdef HAVE_CONFIG_H
+#  include "config.h"
+#endif
+
+#include <simgear/compiler.h>
+
+#include <iostream>
+#include <string>
+#include <sstream>
+
+#include <cmath>    // fabs()
+
+#include "attitude_indicator.hxx"
+#include <Main/fg_props.hxx>
+#include <Main/util.hxx>
+
+using std::string;
+
+AttitudeIndicator::AttitudeIndicator ( SGPropertyNode *node )
+    :
+    _name(node->getStringValue("name", "attitude-indicator")),
+    _num(node->getIntValue("number", 0)),
+    _suction(node->getStringValue("suction", "/systems/vacuum/suction-inhg")),
+    spin_thresh(0.8),
+    max_roll_error(40.0),
+    max_pitch_error(12.0)
+{
+}
+
+AttitudeIndicator::~AttitudeIndicator ()
+{
+}
+
+void
+AttitudeIndicator::init ()
+{
+    string branch;
+    branch = "/instrumentation/" + _name;
+
+    SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
+    SGPropertyNode *n;
+    
+    _pitch_in_node = fgGetNode("/orientation/pitch-deg", true);
+    _roll_in_node = fgGetNode("/orientation/roll-deg", true);
+    _suction_node = fgGetNode(_suction.c_str(), true);
+    SGPropertyNode *cnode = node->getChild("config", 0, true);
+    _tumble_flag_node = cnode->getChild("tumble-flag", 0, true);
+    _caged_node = node->getChild("caged-flag", 0, true);
+    _tumble_node = node->getChild("tumble-norm", 0, true);
+    if( ( n = cnode->getChild("spin-thresh", 0, false ) ) != NULL )
+      spin_thresh = n->getDoubleValue();
+    if( ( n = cnode->getChild("max-roll-error-deg", 0, false ) ) != NULL )
+      max_roll_error = n->getDoubleValue();
+    if( ( n = cnode->getChild("max-pitch-error-deg", 0, false ) ) != NULL )
+      max_pitch_error = n->getDoubleValue();
+    _pitch_int_node = node->getChild("internal-pitch-deg", 0, true);
+    _roll_int_node = node->getChild("internal-roll-deg", 0, true);
+    _pitch_out_node = node->getChild("indicated-pitch-deg", 0, true);
+    _roll_out_node = node->getChild("indicated-roll-deg", 0, true);
+
+    reinit();
+}
+
+void
+AttitudeIndicator::reinit ()
+{
+    _roll_int_node->setDoubleValue(0.0);
+    _pitch_int_node->setDoubleValue(0.0);
+    _gyro.reinit();
+}
+
+void
+AttitudeIndicator::bind ()
+{
+    std::ostringstream temp;
+    string branch;
+    temp << _num;
+    branch = "/instrumentation/" + _name + "[" + temp.str() + "]";
+
+    fgTie((branch + "/serviceable").c_str(),
+          &_gyro, &Gyro::is_serviceable, &Gyro::set_serviceable);
+    fgTie((branch + "/spin").c_str(),
+          &_gyro, &Gyro::get_spin_norm, &Gyro::set_spin_norm);
+}
+
+void
+AttitudeIndicator::unbind ()
+{
+    std::ostringstream temp;
+    string branch;
+    temp << _num;
+    branch = "/instrumentation/" + _name + "[" + temp.str() + "]";
+
+    fgUntie((branch + "/serviceable").c_str());
+    fgUntie((branch + "/spin").c_str());
+}
+
+void
+AttitudeIndicator::update (double dt)
+{
+                                // If it's caged, it doesn't indicate
+    if (_caged_node->getBoolValue()) {
+        _roll_int_node->setDoubleValue(0.0);
+        _pitch_int_node->setDoubleValue(0.0);
+        return;
+    }
+
+                                // Get the spin from the gyro
+    _gyro.set_power_norm(_suction_node->getDoubleValue()/5.0);
+    _gyro.update(dt);
+    double spin = _gyro.get_spin_norm();
+
+                                // Calculate the responsiveness
+    double responsiveness = spin * spin * spin * spin * spin * spin;
+
+                                // Get the indicated roll and pitch
+    double roll = _roll_in_node->getDoubleValue();
+    double pitch = _pitch_in_node->getDoubleValue();
+
+                                // Calculate the tumble for the
+                                // next pass.
+    if (_tumble_flag_node->getBoolValue()) {
+        double tumble = _tumble_node->getDoubleValue();
+        if (fabs(roll) > 45.0) {
+            double target = (fabs(roll) - 45.0) / 45.0;
+            target *= target;   // exponential past +-45 degrees
+            if (roll < 0)
+                target = -target;
+
+            if (fabs(target) > fabs(tumble))
+                tumble = target;
+
+            if (tumble > 1.0)
+                tumble = 1.0;
+            else if (tumble < -1.0)
+                tumble = -1.0;
+        }
+                                    // Reerect in 5 minutes
+        double step = dt/300.0;
+        if (tumble < -step)
+            tumble += step;
+        else if (tumble > step)
+            tumble -= step;
+
+        roll += tumble * 45;
+        _tumble_node->setDoubleValue(tumble);
+    }
+
+    roll = fgGetLowPass(_roll_int_node->getDoubleValue(), roll,
+                        responsiveness);
+    pitch = fgGetLowPass(_pitch_int_node->getDoubleValue(), pitch,
+                         responsiveness);
+
+                                // Assign the new values
+    _roll_int_node->setDoubleValue(roll);
+    _pitch_int_node->setDoubleValue(pitch);
+
+    // add in a gyro underspin "error" if gyro is spinning too slowly
+    double roll_error;
+    double pitch_error;
+    if ( spin <= spin_thresh ) {
+        double roll_error_factor = (spin_thresh - spin) / spin_thresh;
+        double pitch_error_factor = (spin_thresh - spin) / spin_thresh;
+        roll_error = roll_error_factor * roll_error_factor * max_roll_error;
+        pitch_error = pitch_error_factor * pitch_error_factor * max_pitch_error;
+    } else {
+        roll_error = 0.0;
+        pitch_error = 0.0;
+    }
+
+    _roll_out_node->setDoubleValue(roll + roll_error);
+    _pitch_out_node->setDoubleValue(pitch + pitch_error);
+}
+
+
+// Register the subsystem.
+#if 0
+SGSubsystemMgr::InstancedRegistrant<AttitudeIndicator> registrantAttitudeIndicator(
+    SGSubsystemMgr::FDM,
+    {{"instrumentation", SGSubsystemMgr::Dependency::HARD}});
+#endif
+
+// end of attitude_indicator.cxx