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LibrePilot/flight/modules/Airspeed/revolution/gps_airspeed.c

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/**
******************************************************************************
* @addtogroup OpenPilotModules OpenPilot Modules
* @{
* @addtogroup AirspeedModule Airspeed Module
* @brief Use GPS data to estimate airspeed
* @{
*
* @file gps_airspeed.c
* @author The OpenPilot Team, http://www.openpilot.org Copyright (C) 2012.
* @brief Airspeed module, handles temperature and pressure readings from BMP085
*
* @see The GNU Public License (GPL) Version 3
*
*****************************************************************************/
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "openpilot.h"
#include "gps_airspeed.h"
#include "gpsvelocity.h"
#include "attitudeactual.h"
#include "CoordinateConversions.h"
#include <pios_math.h>
// Private constants
#define GPS_AIRSPEED_BIAS_KP 0.1f // Needs to be settable in a UAVO
#define GPS_AIRSPEED_BIAS_KI 0.1f // Needs to be settable in a UAVO
#define SAMPLING_DELAY_MS_GPS 100 // Needs to be settable in a UAVO
#define GPS_AIRSPEED_TIME_CONSTANT_MS 500.0f // Needs to be settable in a UAVO
// Private types
struct GPSGlobals {
float RbeCol1_old[3];
float gpsVelOld_N;
float gpsVelOld_E;
float gpsVelOld_D;
};
// Private variables
static struct GPSGlobals *gps;
// Private functions
/*
* Initialize function loads first data sets, and allocates memory for structure.
*/
void gps_airspeedInitialize()
{
// This method saves memory in case we don't use the GPS module.
gps = (struct GPSGlobals *)pvPortMalloc(sizeof(struct GPSGlobals));
// GPS airspeed calculation variables
GPSVelocityData gpsVelData;
GPSVelocityGet(&gpsVelData);
gps->gpsVelOld_N = gpsVelData.North;
gps->gpsVelOld_E = gpsVelData.East;
gps->gpsVelOld_D = gpsVelData.Down;
AttitudeActualData attData;
AttitudeActualGet(&attData);
float Rbe[3][3];
float q[4] = { attData.q1, attData.q2, attData.q3, attData.q4 };
// Calculate rotation matrix
Quaternion2R(q, Rbe);
gps->RbeCol1_old[0] = Rbe[0][0];
gps->RbeCol1_old[1] = Rbe[0][1];
gps->RbeCol1_old[2] = Rbe[0][2];
}
/*
* Calculate airspeed as a function of GPS groundspeed and vehicle attitude.
* From "IMU Wind Estimation (Theory)", by William Premerlani.
* The idea is that V_gps=V_air+V_wind. If we assume wind constant, =>
* V_gps_2-V_gps_1 = (V_air_2+V_wind_2) -(V_air_1+V_wind_1) = V_air_2 - V_air_1.
* If we assume airspeed constant, => V_gps_2-V_gps_1 = |V|*(f_2 - f1),
* where "f" is the fuselage vector in earth coordinates.
* We then solve for |V| = |V_gps_2-V_gps_1|/ |f_2 - f1|.
*/
void gps_airspeedGet(float *v_air_GPS)
{
float Rbe[3][3];
{ // Scoping to save memory. We really just need Rbe.
AttitudeActualData attData;
AttitudeActualGet(&attData);
float q[4] = { attData.q1, attData.q2, attData.q3, attData.q4 };
// Calculate rotation matrix
Quaternion2R(q, Rbe);
}
// Calculate the cos(angle) between the two fuselage basis vectors
float cosDiff = (Rbe[0][0] * gps->RbeCol1_old[0]) + (Rbe[0][1] * gps->RbeCol1_old[1]) + (Rbe[0][2] * gps->RbeCol1_old[2]);
// If there's more than a 5 degree difference between two fuselage measurements, then we have sufficient delta to continue.
if (fabsf(cosDiff) < cosf(DEG2RAD(5.0f))) {
GPSVelocityData gpsVelData;
GPSVelocityGet(&gpsVelData);
// Calculate the norm^2 of the difference between the two GPS vectors
float normDiffGPS2 = powf(gpsVelData.North - gps->gpsVelOld_N, 2.0f) + powf(gpsVelData.East - gps->gpsVelOld_E, 2.0f) + powf(gpsVelData.Down - gps->gpsVelOld_D, 2.0f);
// Calculate the norm^2 of the difference between the two fuselage vectors
float normDiffAttitude2 = powf(Rbe[0][0] - gps->RbeCol1_old[0], 2.0f) + powf(Rbe[0][1] - gps->RbeCol1_old[1], 2.0f) + powf(Rbe[0][2] - gps->RbeCol1_old[2], 2.0f);
// Airspeed magnitude is the ratio between the two difference norms
*v_air_GPS = sqrtf(normDiffGPS2 / normDiffAttitude2);
// Save old variables for next pass
gps->gpsVelOld_N = gpsVelData.North;
gps->gpsVelOld_E = gpsVelData.East;
gps->gpsVelOld_D = gpsVelData.Down;
gps->RbeCol1_old[0] = Rbe[0][0];
gps->RbeCol1_old[1] = Rbe[0][1];
gps->RbeCol1_old[2] = Rbe[0][2];
} else {}
}
/**
* @}
* @}
*/