ardupilot/libraries/SITL/SIM_Aircraft.cpp

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
   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, see <http://www.gnu.org/licenses/>.
 */
/*
  parent class for aircraft simulators
*/

#include <AP_Common.h>
#include "SIM_Aircraft.h"
#include <unistd.h>
#include <sys/time.h>
#include <stdio.h>

/*
  parent class for all simulator types
 */

/*
  constructor
 */
Aircraft::Aircraft(const char *home_str, const char *frame_str) :
    ground_level(0),
    frame_height(0),
    dcm(),
    gyro(),
    velocity_ef(),
    mass(0),
    accel_body(0, 0, -GRAVITY_MSS),
    time_now_us(0),
    gyro_noise(radians(0.1f)),
    accel_noise(0.3),
    rate_hz(400)
{
    char *saveptr=NULL;
    char *s = strdup(home_str);
    char *lat_s = strtok_r(s, ",", &saveptr);
    char *lon_s = strtok_r(NULL, ",", &saveptr);
    char *alt_s = strtok_r(NULL, ",", &saveptr);
    char *yaw_s = strtok_r(NULL, ",", &saveptr);

    memset(&home, 0, sizeof(home));
    home.lat = atof(lat_s) * 1.0e7;
    home.lng = atof(lon_s) * 1.0e7;
    home.alt = atof(alt_s) * 1.0e2;
    location = home;
    ground_level = home.alt*0.01;

    dcm.from_euler(0, 0, atof(yaw_s));
    free(s);

    set_speedup(1);
}

/* 
   return true if we are on the ground 
*/
bool Aircraft::on_ground(const Vector3f &pos) const
{
    return (-pos.z) + home.alt*0.01f <= ground_level + frame_height;
}

/* 
   update location from position 
*/
void Aircraft::update_position(void)
{
    float bearing = degrees(atan2f(position.y, position.x));
    float distance = sqrtf(sq(position.x) + sq(position.y));

    location = home;
    location_update(location, bearing, distance);

    location.alt  = home.alt - position.z*100.0f;

    time_now_us += frame_time_us;
    sync_frame_time();
}

/* 
   rotate to the given yaw 
*/
void Aircraft::set_yaw_degrees(float yaw_degrees)
{
    float roll, pitch, yaw;
    dcm.to_euler(&roll, &pitch, &yaw);

    yaw = radians(yaw_degrees);
    dcm.from_euler(roll, pitch, yaw);
}
        
/* advance time by deltat in seconds */
void Aircraft::time_advance(float deltat)
{
    time_now_us += deltat * 1.0e6f;
}

/* setup the frame step time */
void Aircraft::setup_frame_time(float new_rate, float new_speedup)
{
    rate_hz = new_rate;
    target_speedup = new_speedup;
    frame_time_us = 1.0e6f/rate_hz;

    scaled_frame_time_us = frame_time_us/target_speedup;
    last_wall_time_us = get_wall_time_us();
    achieved_rate_hz = rate_hz;
}

/* adjust frame_time calculation */
void Aircraft::adjust_frame_time(float new_rate)
{
    rate_hz = new_rate;
    frame_time_us = 1.0e6f/rate_hz;
    scaled_frame_time_us = frame_time_us/target_speedup;
}

/* try to synchronise simulation time with wall clock time, taking
   into account desired speedup */
void Aircraft::sync_frame_time(void)
{
    uint64_t now = get_wall_time_us();
    uint64_t dt_us = now - last_wall_time_us;
    if (dt_us < scaled_frame_time_us) {
        usleep(scaled_frame_time_us - dt_us);
        now = get_wall_time_us();

        if (now > last_wall_time_us && now - last_wall_time_us < 1.0e5) {
            float rate = 1.0e6f/(now - last_wall_time_us);
            achieved_rate_hz = (0.98f*achieved_rate_hz) + (0.02f*rate);
            if (achieved_rate_hz < rate_hz * target_speedup) {
                scaled_frame_time_us *= 0.999;
            } else {
                scaled_frame_time_us *= 1.001;
            }
        }

    }
    last_wall_time_us = now;
}

/* add noise based on throttle level (from 0..1) */
void Aircraft::add_noise(float throttle)
{
    gyro += Vector3f(rand_normal(0, 1),
                     rand_normal(0, 1),
                     rand_normal(0, 1)) * gyro_noise * throttle;
    accel_body += Vector3f(rand_normal(0, 1),
                           rand_normal(0, 1),
                           rand_normal(0, 1)) * accel_noise * throttle;
}

/*
  normal distribution random numbers
  See
  http://en.literateprograms.org/index.php?title=Special:DownloadCode/Box-Muller_transform_%28C%29&oldid=7011
*/
double Aircraft::rand_normal(double mean, double stddev)
{
    static double n2 = 0.0;
    static int n2_cached = 0;
    if (!n2_cached)
    {
        double x, y, r;
        do
        {
            x = 2.0*rand()/RAND_MAX - 1;
            y = 2.0*rand()/RAND_MAX - 1;

            r = x*x + y*y;
        }
        while (r == 0.0 || r > 1.0);
        {
            double d = sqrt(-2.0*log(r)/r);
            double n1 = x*d;
            n2 = y*d;
            double result = n1*stddev + mean;
            n2_cached = 1;
            return result;
        }
    }
    else
    {
        n2_cached = 0;
        return n2*stddev + mean;
    }
}




/* 
   fill a sitl_fdm structure from the simulator state 
*/
void Aircraft::fill_fdm(struct sitl_fdm &fdm) const
{
    fdm.timestamp_us = time_now_us;
    fdm.latitude  = location.lat * 1.0e-7;
    fdm.longitude = location.lng * 1.0e-7;
    fdm.altitude  = location.alt * 1.0e-2;
    fdm.heading   = degrees(atan2f(velocity_ef.y, velocity_ef.x));
    fdm.speedN    = velocity_ef.x;
    fdm.speedE    = velocity_ef.y;
    fdm.speedD    = velocity_ef.z;
    fdm.xAccel    = accel_body.x;
    fdm.yAccel    = accel_body.y;
    fdm.zAccel    = accel_body.z;
    Vector3f gyro_ef = SITL::convert_earth_frame(dcm, gyro);
    fdm.rollRate  = degrees(gyro_ef.x);
    fdm.pitchRate = degrees(gyro_ef.y);
    fdm.yawRate   = degrees(gyro_ef.z);
    float r, p, y;
    dcm.to_euler(&r, &p, &y);
    fdm.rollDeg  = degrees(r);
    fdm.pitchDeg = degrees(p);
    fdm.yawDeg   = degrees(y);
    fdm.airspeed = velocity_ef.length();
    fdm.magic = 0x4c56414f;
}

uint64_t Aircraft::get_wall_time_us() const
{
	struct timeval tp;
	gettimeofday(&tp,NULL);
	return tp.tv_sec*1.0e6 + tp.tv_usec;
}

/*
  set simulation speedup
 */
void Aircraft::set_speedup(float speedup)
{
    setup_frame_time(rate_hz, speedup);
}