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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
#include "Compass.h"
// Default constructor.
// Note that the Vector/Matrix constructors already implicitly zero
// their values.
//
Compass::Compass(void) :
product_id(AP_COMPASS_TYPE_UNKNOWN),
_declination (0.0),
_learn(1),
_use_for_yaw(1),
_null_enable(false),
_null_init_done(false),
_auto_declination(1),
_orientation(ROTATION_NONE)
{
}
// Default init method, just returns success.
//
bool
Compass::init()
{
return true;
}
/* set_orientation
void
Compass::set_orientation(enum Rotation rotation)
{
_orientation = rotation;
}
*/
/* set_offsets
void
Compass::set_offsets(const Vector3f &offsets)
{
_offset.set(offsets);
}
*/
/* save_offsets
void
Compass::save_offsets()
{
_offset.save();
}
*/
/* get_offsets
Vector3f &
Compass::get_offsets()
{
return _offset;
}
*/
/* set_initial_location
void
Compass::set_initial_location(long latitude, long longitude)
{
// if automatic declination is configured, then compute
// the declination based on the initial GPS fix
if (_auto_declination) {
// Set the declination based on the lat/lng from GPS
null_offsets_disable();
_declination.set(radians(AP_Declination::get_declination((float)latitude / 10000000, (float)longitude / 10000000)));
null_offsets_enable();
}
}
*/
/* set_declination
void
Compass::set_declination(float radians)
{
_declination.set_and_save(radians);
}
*/
/* get_declination
float
Compass::get_declination()
{
return _declination.get();
}
*/
/* calculate
void
Compass::calculate(float roll, float pitch)
{
// Note - This function implementation is deprecated
// The alternate implementation of this function using the dcm matrix is preferred
float headX;
float headY;
float cos_roll;
float sin_roll;
float cos_pitch;
float sin_pitch;
cos_roll = cos(roll);
sin_roll = sin(roll);
cos_pitch = cos(pitch);
sin_pitch = sin(pitch);
// Tilt compensated magnetic field X component:
headX = mag_x*cos_pitch + mag_y*sin_roll*sin_pitch + mag_z*cos_roll*sin_pitch;
// Tilt compensated magnetic field Y component:
headY = mag_y*cos_roll - mag_z*sin_roll;
// magnetic heading
heading = atan2(-headY,headX);
// Declination correction (if supplied)
if( fabs(_declination) > 0.0 )
{
heading = heading + _declination;
if (heading > M_PI) // Angle normalization (-180 deg, 180 deg)
heading -= (2.0 * M_PI);
else if (heading < -M_PI)
heading += (2.0 * M_PI);
}
// Optimization for external DCM use. Calculate normalized components
heading_x = cos(heading);
heading_y = sin(heading);
}
*/
void
Compass::calculate(const Matrix3f &dcm_matrix)
{
float headX;
float headY;
float cos_pitch = safe_sqrt(1-(dcm_matrix.c.x*dcm_matrix.c.x));
// sin(pitch) = - dcm_matrix(3,1)
// cos(pitch)*sin(roll) = - dcm_matrix(3,2)
// cos(pitch)*cos(roll) = - dcm_matrix(3,3)
if (cos_pitch == 0.0) {
// we are pointing straight up or down so don't update our
// heading using the compass. Wait for the next iteration when
// we hopefully will have valid values again.
return;
}
// Tilt compensated magnetic field X component:
headX = mag_x*cos_pitch - mag_y*dcm_matrix.c.y*dcm_matrix.c.x/cos_pitch - mag_z*dcm_matrix.c.z*dcm_matrix.c.x/cos_pitch;
// Tilt compensated magnetic field Y component:
headY = mag_y*dcm_matrix.c.z/cos_pitch - mag_z*dcm_matrix.c.y/cos_pitch;
// magnetic heading
// 6/4/11 - added constrain to keep bad values from ruining DCM Yaw - Jason S.
heading = constrain(atan2(-headY,headX), -3.15, 3.15);
// Declination correction (if supplied)
if( fabs(_declination) > 0.0 )
{
heading = heading + _declination;
if (heading > M_PI) // Angle normalization (-180 deg, 180 deg)
heading -= (2.0 * M_PI);
else if (heading < -M_PI)
heading += (2.0 * M_PI);
}
// Optimization for external DCM use. Calculate normalized components
heading_x = cos(heading);
heading_y = sin(heading);
#if 0
if (isnan(heading_x) || isnan(heading_y)) {
Serial.printf("COMPASS: c.x %f c.y %f c.z %f cos_pitch %f mag_x %d mag_y %d mag_z %d headX %f headY %f heading %f heading_x %f heading_y %f\n",
dcm_matrix.c.x,
dcm_matrix.c.y,
dcm_matrix.c.x,
cos_pitch,
(int)mag_x, (int)mag_y, (int)mag_z,
headX, headY,
heading,
heading_x, heading_y);
}
#endif
}
/*
this offset nulling algorithm is inspired by this paper from Bill Premerlani
http://gentlenav.googlecode.com/files/MagnetometerOffsetNullingRevisited.pdf
The base algorithm works well, but is quite sensitive to
noise. After long discussions with Bill, the following changes were
made:
1) we keep a history buffer that effectively divides the mag
vectors into a set of N streams. The algorithm is run on the
streams separately
2) within each stream we only calculate a change when the mag
vector has changed by a significant amount.
This gives us the property that we learn quickly if there is no
noise, but still learn correctly (and slowly) in the face of lots of
noise.
*/
/* null_offsets
void
Compass::null_offsets(void)
{
if (_null_enable == false || _learn == 0) {
// auto-calibration is disabled
return;
}
// this gain is set so we converge on the offsets in about 5
// minutes with a 10Hz compass
const float gain = 0.01;
const float max_change = 10.0;
const float min_diff = 50.0;
Vector3f ofs;
ofs = _offset.get();
if (!_null_init_done) {
// first time through
_null_init_done = true;
for (uint8_t i=0; i<_mag_history_size; i++) {
// fill the history buffer with the current mag vector,
// with the offset removed
_mag_history[i] = Vector3i((mag_x+0.5) - ofs.x, (mag_y+0.5) - ofs.y, (mag_z+0.5) - ofs.z);
}
_mag_history_index = 0;
return;
}
Vector3f b1, b2, diff;
float length;
// get a past element
b1 = Vector3f(_mag_history[_mag_history_index].x,
_mag_history[_mag_history_index].y,
_mag_history[_mag_history_index].z);
// the history buffer doesn't have the offsets
b1 += ofs;
// get the current vector
b2 = Vector3f(mag_x, mag_y, mag_z);
// calculate the delta for this sample
diff = b2 - b1;
length = diff.length();
if (length < min_diff) {
// the mag vector hasn't changed enough - we don't get
// enough information from this vector to use it.
// Note that we don't put the current vector into the mag
// history here. We want to wait for a larger rotation to
// build up before calculating an offset change, as accuracy
// of the offset change is highly dependent on the size of the
// rotation.
_mag_history_index = (_mag_history_index + 1) % _mag_history_size;
return;
}
// put the vector in the history
_mag_history[_mag_history_index] = Vector3i((mag_x+0.5) - ofs.x, (mag_y+0.5) - ofs.y, (mag_z+0.5) - ofs.z);
_mag_history_index = (_mag_history_index + 1) % _mag_history_size;
// equation 6 of Bills paper
diff = diff * (gain * (b2.length() - b1.length()) / length);
// limit the change from any one reading. This is to prevent
// single crazy readings from throwing off the offsets for a long
// time
length = diff.length();
if (length > max_change) {
diff *= max_change / length;
}
// set the new offsets
_offset.set(_offset.get() - diff);
}
*/
// Have no idea why this is necessary:
bool Compass::read(void) {
return false;
}
void
Compass::null_offsets_enable(void)
{
_null_init_done = false;
_null_enable = true;
}
void
Compass::null_offsets_disable(void)
{
_null_init_done = false;
_null_enable = false;
}