/****************************************************************************
 *
 *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
 *   Author: Thomas Gubler <thomasgubler@student.ethz.ch>
 *           Julian Oes <joes@student.ethz.ch>
 *           Lorenz Meier <lm@inf.ethz.ch>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/**
 * @file geo.c
 *
 * Geo / math functions to perform geodesic calculations
 *
 * @author Thomas Gubler <thomasgubler@student.ethz.ch>
 * @author Julian Oes <joes@student.ethz.ch>
 * @author Lorenz Meier <lm@inf.ethz.ch>
 */

#include <systemlib/geo/geo.h>
#include <math.h>

__EXPORT float get_distance_to_next_waypoint(double lat_now, double lon_now, double lat_next, double lon_next)
{
	double lat_now_rad = lat_now / 180.0 * M_PI;
	double lon_now_rad = lon_now / 180.0 * M_PI;
	double lat_next_rad = lat_next / 180.0 * M_PI;
	double lon_next_rad = lon_next / 180.0 * M_PI;


	double d_lat = lat_next_rad - lat_now_rad;
	double d_lon = lon_next_rad - lon_now_rad;

	double a = sin(d_lat / 2.0) * sin(d_lat / 2.0) + sin(d_lon / 2.0) * sin(d_lon / 2.0) * cos(lat_now_rad) * cos(lat_next_rad);
	double c = 2 * atan2(sqrt(a), sqrt(1 - a));

	const double radius_earth = 6371000.0;

	return radius_earth * c;
}

__EXPORT float get_bearing_to_next_waypoint(double lat_now, double lon_now, double lat_next, double lon_next)
{
	double lat_now_rad = lat_now / 180.0 * M_PI;
	double lon_now_rad = lon_now / 180.0 * M_PI;
	double lat_next_rad = lat_next / 180.0 * M_PI;
	double lon_next_rad = lon_next / 180.0 * M_PI;

	double d_lat = lat_next_rad - lat_now_rad;
	double d_lon = lon_next_rad - lon_now_rad;

	/* conscious mix of double and float trig function to maximize speed and efficiency */
	float theta = atan2f(sin(d_lon) * cos(lat_next_rad) , cos(lat_now_rad) * sin(lat_next_rad) - sin(lat_now_rad) * cos(lat_next_rad) * cos(d_lon));

	// XXX wrapping check is incomplete
	if (theta < 0.0f) {
		theta = theta + 2.0f * M_PI_F;
	}

	return theta;
}