ardupilot/libraries/AP_AHRS/AP_AHRS.cpp

/*
	APM_AHRS.cpp

	This library is free software; you can redistribute it and/or
	modify it under the terms of the GNU Lesser General Public License
	as published by the Free Software Foundation; either version 2.1
	of the License, or (at your option) any later version.
*/
#include <FastSerial.h>
#include <AP_AHRS.h>


// table of user settable parameters
const AP_Param::GroupInfo AP_AHRS::var_info[] PROGMEM = {
	// index 0 and 1 are for old parameters that are no longer used

    // @Param: GPS_GAIN
    // @DisplayName: AHRS GPS gain
    // @Description: This controls how how much to use the GPS to correct the attitude. This should never be set to zero for a plane as it would result in the plane losing control in turns. For a plane please use the default value of 1.0.
    // @Range: 0.0 1.0
    // @Increment: .01
    AP_GROUPINFO("GPS_GAIN",  2, AP_AHRS, gps_gain, 1.0),

    // @Param: GPS_USE
    // @DisplayName: AHRS use GPS for navigation
    // @Description: This controls whether to use dead-reckoning or GPS based navigation. If set to 0 then the GPS won't be used for navigation, and only dead reckoning will be used. A value of zero should never be used for normal flight.
    // @User: Advanced
    AP_GROUPINFO("GPS_USE",  3, AP_AHRS, _gps_use, 1),

    // @Param: YAW_P
    // @DisplayName: Yaw P
    // @Description: This controls the weight the compass or GPS has on the heading. A higher value means the heading will track the yaw source (GPS or compass) more rapidly.
    // @Range: 0.1 0.4
    // @Increment: .01
    AP_GROUPINFO("YAW_P", 4,    AP_AHRS, _kp_yaw, 0.4),

    // @Param: RP_P
    // @DisplayName: AHRS RP_P
    // @Description: This controls how fast the accelerometers correct the attitude
    // @Range: 0.1 0.4
    // @Increment: .01
    AP_GROUPINFO("RP_P",  5,    AP_AHRS, _kp, 0.4),

    // @Param: WIND_MAX
    // @DisplayName: Maximum wind
    // @Description: This sets the maximum allowable difference between ground speed and airspeed. This allows the plane to cope with a failing airspeed sensor. A value of zero means to use the airspeed as is.
    // @Range: 0 127
    // QUnits: m/s
    // @Increment: 1
    AP_GROUPINFO("WIND_MAX",  6,    AP_AHRS, _wind_max, 0.0),

    // @Param: BARO_USE
    // @DisplayName: AHRS Use Barometer
    // @Description: This controls the use of the barometer for vertical acceleration compensation in AHRS. It is currently recommended that you set this value to zero unless you are a developer experimenting with the AHRS system.
    // @Values: 0:Disabled,1:Enabled
    // @User: Advanced
    AP_GROUPINFO("BARO_USE",  7,    AP_AHRS, _baro_use, 0),

    // @Param: TRIM
    // @DisplayName: AHRS Trim
    // @Description: Compensates for the difference between the control board and the frame
    // @Units: Radians
    // @User: Advanced
    AP_GROUPINFO("TRIM", 8, AP_AHRS, _trim, 0),

    AP_GROUPEND
};

// get pitch rate in earth frame, in radians/s
float AP_AHRS::get_pitch_rate_earth(void) 
{
	Vector3f omega = get_gyro();
	return cos(roll) * omega.y - sin(roll) * omega.z;
}

// get roll rate in earth frame, in radians/s
float AP_AHRS::get_roll_rate_earth(void)  {
	Vector3f omega = get_gyro();
	return omega.x + tan(pitch)*(omega.y*sin(roll) + omega.z*cos(roll));
}

// return airspeed estimate if available
bool AP_AHRS::airspeed_estimate(float *airspeed_ret)
{
	if (_airspeed && _airspeed->use()) {
		*airspeed_ret = _airspeed->get_airspeed();
		if (_wind_max > 0 && _gps && _gps->status() == GPS::GPS_OK) {
			// constrain the airspeed by the ground speed
			// and AHRS_WIND_MAX
			*airspeed_ret = constrain(*airspeed_ret, 
						  _gps->ground_speed*0.01 - _wind_max, 
						  _gps->ground_speed*0.01 + _wind_max);
		}
		return true;
	}
	return false;
}

// add_trim - adjust the roll and pitch trim up to a total of 10 degrees
void AP_AHRS::add_trim(float roll_in_radians, float pitch_in_radians)
{
    Vector3f trim = _trim.get();

    // debug -- remove me!
    Serial.printf_P(PSTR("\nadd_trim before R:%4.2f P:%4.2f\n"),ToDeg(trim.x),ToDeg(trim.y));

    // add new trim
    trim.x = constrain(trim.x + roll_in_radians, ToRad(-10.0), ToRad(10.0));
    trim.y = constrain(trim.y + pitch_in_radians, ToRad(-10.0), ToRad(10.0));

    // set and save new trim values
    _trim.set_and_save(trim);

    // debug -- remove me!
    Serial.printf_P(PSTR("add_trim after R:%4.2f P:%4.2f\n"),ToDeg(trim.x),ToDeg(trim.y));
}