175 lines
6 KiB
C++
175 lines
6 KiB
C++
// mag_compass.cxx - a magnetic compass.
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// Written by David Megginson, started 2003.
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//
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// This file is in the Public Domain and comes with no warranty.
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// This implementation is derived from an earlier one by Alex Perry,
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// which appeared in src/Cockpit/steam.cxx
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include <simgear/sg_inlines.h>
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#include "mag_compass.hxx"
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#include <Main/fg_props.hxx>
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#include <Main/util.hxx>
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MagCompass::MagCompass ( SGPropertyNode *node )
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: _error_deg(0.0),
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_rate_degps(0.0),
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_name(node->getStringValue("name", "magnetic-compass")),
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_num(node->getIntValue("number", 0))
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{
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}
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MagCompass::~MagCompass ()
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{
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}
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void
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MagCompass::init ()
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{
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string branch;
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branch = "/instrumentation/" + _name;
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SGPropertyNode *node = fgGetNode(branch.c_str(), _num, true );
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_serviceable_node = node->getChild("serviceable", 0, true);
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_roll_node = fgGetNode("/orientation/roll-deg", true);
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_pitch_node = fgGetNode("/orientation/pitch-deg", true);
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_heading_node = fgGetNode("/orientation/heading-magnetic-deg", true);
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_beta_node = fgGetNode("/orientation/side-slip-deg", true);
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_dip_node = fgGetNode("/environment/magnetic-dip-deg", true);
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_x_accel_node = fgGetNode("/accelerations/pilot/x-accel-fps_sec", true);
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_y_accel_node = fgGetNode("/accelerations/pilot/y-accel-fps_sec", true);
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_z_accel_node = fgGetNode("/accelerations/pilot/z-accel-fps_sec", true);
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_out_node = node->getChild("indicated-heading-deg", 0, true);
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}
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void
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MagCompass::update (double delta_time_sec)
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{
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// This is the real magnetic
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// which would be displayed
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// if the compass had no errors.
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//double heading_mag_deg = _heading_node->getDoubleValue();
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// don't update if the compass
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// is broken
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if (!_serviceable_node->getBoolValue())
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return;
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/*
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* Vassilii: commented out because this way, even when parked,
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* w/o any accelerations and level, the compass is jammed.
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* If somebody wants to model jamming, real forces (i.e. accelerations)
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* and not sideslip angle must be considered.
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*/
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#if 0
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// jam on excessive sideslip
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if (fabs(_beta_node->getDoubleValue()) > 12.0) {
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_rate_degps = 0.0;
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return;
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}
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#endif
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/*
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Formula for northernly turning error from
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http://williams.best.vwh.net/compass/node4.html:
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Hc: compass heading
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psi: magnetic heading
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theta: bank angle (right positive; should be phi here)
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mu: dip angle (down positive)
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Hc = atan2(sin(Hm)cos(theta)-tan(mu)sin(theta), cos(Hm))
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This function changes the variable names to the more common psi
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for the heading, theta for the pitch, and phi for the roll (and
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target_deg for Hc). It also modifies the equation to
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incorporate pitch as well as roll, as suggested by Chris
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Metzler.
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*/
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// bank angle (radians)
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double phi = _roll_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
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// pitch angle (radians)
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double theta = _pitch_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
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// magnetic heading (radians)
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double psi = _heading_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
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// magnetic dip (radians)
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double mu = _dip_node->getDoubleValue() * SGD_DEGREES_TO_RADIANS;
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/*
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Tilt adjustments for accelerations.
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The magnitudes of these are totally made up, but in real life,
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they would depend on the fluid level, the amount of friction,
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etc. anyway. Basically, the compass float tilts forward for
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acceleration and backward for deceleration. Tilt about 4
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degrees (0.07 radians) for every G (32 fps/sec) of
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acceleration.
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TODO: do something with the vertical acceleration.
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*/
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double x_accel_g = _x_accel_node->getDoubleValue() / 32;
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double y_accel_g = _y_accel_node->getDoubleValue() / 32;
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//double z_accel_g = _z_accel_node->getDoubleValue() / 32;
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theta -= 0.07 * x_accel_g;
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phi -= 0.07 * y_accel_g;
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////////////////////////////////////////////////////////////////////
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// calculate target compass heading degrees
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////////////////////////////////////////////////////////////////////
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// these are expensive: don't repeat
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double sin_phi = sin(phi);
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double sin_theta = sin(theta);
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double sin_mu = sin(mu);
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double cos_theta = cos(theta);
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double cos_psi = cos(psi);
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double cos_mu = cos(mu);
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double a = cos(phi) * sin(psi) * cos_mu
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- sin_phi * cos_theta * sin_mu
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- sin_phi* sin_theta * cos_mu * cos_psi;
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double b = cos_theta * cos_psi * cos(mu)
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- sin_theta * sin_mu;
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// This is the value that the compass
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// is *trying* to display.
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double target_deg = atan2(a, b) * SGD_RADIANS_TO_DEGREES;
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double old_deg = _out_node->getDoubleValue();
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while ((target_deg - old_deg) > 180.0)
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target_deg -= 360.0;
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while ((target_deg - old_deg) < -180.0)
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target_deg += 360.0;
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// The compass has a current rate of
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// rotation -- move the rate of rotation
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// towards one that will turn the compass
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// to the correct heading, but lag a bit.
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// (so that the compass can keep overshooting
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// and coming back).
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double error = target_deg - old_deg;
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_rate_degps = fgGetLowPass(_rate_degps, error, delta_time_sec / 5.0);
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double indicated_deg = old_deg + _rate_degps * delta_time_sec;
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SG_NORMALIZE_RANGE(indicated_deg, 0.0, 360.0);
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// That's it -- set the messed-up heading.
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_out_node->setDoubleValue(indicated_deg);
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}
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// end of altimeter.cxx
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