gps_helper.cpp

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#include "gps_helper.h"
#include <math.h>

#ifndef M_PI
#define M_PI        3.141592653589793238462643383280
#endif


/**
 * @file gps_helper.cpp
 *
 * @author Thomas Gubler <thomasgubler@student.ethz.ch>
 * @author Julian Oes <julian@oes.ch>
 */

GPSHelper::GPSHelper(GPSCallbackPtr callback, void *callback_user)
    : _callback(callback), _callback_user(callback_user)
{
}

void
GPSHelper::resetUpdateRates()
{
    _rate_count_vel = 0;
    _rate_count_lat_lon = 0;
    _interval_rate_start = gps_absolute_time();
}

void
GPSHelper::storeUpdateRates()
{
    _rate_vel = _rate_count_vel / (((float)(gps_absolute_time() - _interval_rate_start)) / 1000000.0f);
    _rate_lat_lon = _rate_count_lat_lon / (((float)(gps_absolute_time() - _interval_rate_start)) / 1000000.0f);
}

void GPSHelper::ECEF2lla(double ecef_x, double ecef_y, double ecef_z, double &latitude, double &longitude,
             float &altitude)
{
    // WGS84 ellipsoid constants
    constexpr double a = 6378137.; // radius
    constexpr double e = 8.1819190842622e-2;  // eccentricity

    constexpr double asq = a * a;
    constexpr double esq = e * e;

    double x = ecef_x;
    double y = ecef_y;
    double z = ecef_z;

    double b = sqrt(asq * (1. - esq));
    double bsq = b * b;
    double ep = sqrt((asq - bsq) / bsq);
    double p = sqrt(x * x + y * y);
    double th = atan2(a * z, b * p);

    longitude = atan2(y, x);
    double sin_th = sin(th);
    double cos_th = cos(th);
    latitude = atan2(z + ep * ep * b * sin_th * sin_th * sin_th, p - esq * a * cos_th * cos_th * cos_th);
    double sin_lat = sin(latitude);
    double N = a / sqrt(1. - esq * sin_lat * sin_lat);
    altitude = (float)(p / cos(latitude) - N);

    // rad to deg
    longitude *= 180. / M_PI;
    latitude *= 180. / M_PI;

    // correction for altitude near poles left out.
}