/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
* location.cpp
* Copyright (C) Andrew Tridgell 2011
*
* This file 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 file 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 .
*/
/*
* this module deals with calculations involving struct Location
*/
#include
#include "AP_Math.h"
// radius of earth in meters
#define RADIUS_OF_EARTH 6378100
// scaling factor from 1e-7 degrees to meters at equater
// == 1.0e-7 * DEG_TO_RAD * RADIUS_OF_EARTH
#define LOCATION_SCALING_FACTOR 0.011131884502145034f
// inverse of LOCATION_SCALING_FACTOR
#define LOCATION_SCALING_FACTOR_INV 89.83204953368922f
float longitude_scale(const struct Location &loc)
{
static int32_t last_lat;
static float scale = 1.0;
if (labs(last_lat - loc.lat) < 100000) {
// we are within 0.01 degrees (about 1km) of the
// same latitude. We can avoid the cos() and return
// the same scale factor.
return scale;
}
scale = cosf(loc.lat * 1.0e-7f * DEG_TO_RAD);
last_lat = loc.lat;
return scale;
}
// return distance in meters between two locations
float get_distance(const struct Location &loc1, const struct Location &loc2)
{
float dlat = (float)(loc2.lat - loc1.lat);
float dlong = ((float)(loc2.lng - loc1.lng)) * longitude_scale(loc2);
return pythagorous2(dlat, dlong) * LOCATION_SCALING_FACTOR;
}
// return distance in centimeters to between two locations
uint32_t get_distance_cm(const struct Location &loc1, const struct Location &loc2)
{
return get_distance(loc1, loc2) * 100;
}
// return bearing in centi-degrees between two locations
int32_t get_bearing_cd(const struct Location &loc1, const struct Location &loc2)
{
int32_t off_x = loc2.lng - loc1.lng;
int32_t off_y = (loc2.lat - loc1.lat) / longitude_scale(loc2);
int32_t bearing = 9000 + atan2f(-off_y, off_x) * 5729.57795f;
if (bearing < 0) bearing += 36000;
return bearing;
}
// see if location is past a line perpendicular to
// the line between point1 and point2. If point1 is
// our previous waypoint and point2 is our target waypoint
// then this function returns true if we have flown past
// the target waypoint
bool location_passed_point(const struct Location &location,
const struct Location &point1,
const struct Location &point2)
{
// the 3 points form a triangle. If the angle between lines
// point1->point2 and location->point2 is greater than 90
// degrees then we have passed the waypoint
Vector2f loc1(location.lat, location.lng);
Vector2f pt1(point1.lat, point1.lng);
Vector2f pt2(point2.lat, point2.lng);
float angle = (loc1 - pt2).angle(pt1 - pt2);
if (isinf(angle)) {
// two of the points are co-located.
// If location is equal to point2 then say we have passed the
// waypoint, otherwise say we haven't
if (get_distance(location, point2) == 0) {
return true;
}
return false;
} else if (angle == 0) {
// if we are exactly on the line between point1 and
// point2 then we are past the waypoint if the
// distance from location to point1 is greater then
// the distance from point2 to point1
return get_distance(location, point1) >
get_distance(point2, point1);
}
if (degrees(angle) > 90) {
return true;
}
return false;
}
/*
* extrapolate latitude/longitude given bearing and distance
* Note that this function is accurate to about 1mm at a distance of
* 100m. This function has the advantage that it works in relative
* positions, so it keeps the accuracy even when dealing with small
* distances and floating point numbers
*/
void location_update(struct Location &loc, float bearing, float distance)
{
float ofs_north = cosf(radians(bearing))*distance;
float ofs_east = sinf(radians(bearing))*distance;
location_offset(loc, ofs_north, ofs_east);
}
/*
* extrapolate latitude/longitude given distances north and east
* This function costs about 80 usec on an AVR2560
*/
void location_offset(struct Location &loc, float ofs_north, float ofs_east)
{
if (ofs_north != 0 || ofs_east != 0) {
int32_t dlat = ofs_north * LOCATION_SCALING_FACTOR_INV;
int32_t dlng = (ofs_east * LOCATION_SCALING_FACTOR_INV) / longitude_scale(loc);
loc.lat += dlat;
loc.lng += dlng;
}
}
/*
return the distance in meters in North/East plane as a N/E vector
from loc1 to loc2
*/
Vector2f location_diff(const struct Location &loc1, const struct Location &loc2)
{
return Vector2f((loc2.lat - loc1.lat) * LOCATION_SCALING_FACTOR,
(loc2.lng - loc1.lng) * LOCATION_SCALING_FACTOR * longitude_scale(loc1));
}
/*
wrap an angle in centi-degrees to 0..36000
*/
int32_t wrap_360_cd(int32_t error)
{
while (error > 36000) error -= 36000;
while (error < 0) error += 36000;
return error;
}
/*
wrap an angle in centi-degrees to -18000..18000
*/
int32_t wrap_180_cd(int32_t error)
{
while (error > 18000) error -= 36000;
while (error < -18000) error += 36000;
return error;
}
/*
wrap an angle defined in radians to -PI ~ PI (equivalent to +- 180 degrees)
*/
float wrap_PI(float angle_in_radians)
{
while (angle_in_radians > PI) angle_in_radians -= 2.0f*PI;
while (angle_in_radians < -PI) angle_in_radians += 2.0f*PI;
return angle_in_radians;
}
/*
print a int32_t lat/long in decimal degrees
*/
void print_latlon(AP_HAL::BetterStream *s, int32_t lat_or_lon)
{
int32_t dec_portion, frac_portion;
int32_t abs_lat_or_lon = labs(lat_or_lon);
// extract decimal portion (special handling of negative numbers to ensure we round towards zero)
dec_portion = abs_lat_or_lon / 10000000UL;
// extract fractional portion
frac_portion = abs_lat_or_lon - dec_portion*10000000UL;
// print output including the minus sign
if( lat_or_lon < 0 ) {
s->printf_P(PSTR("-"));
}
s->printf_P(PSTR("%ld.%07ld"),(long)dec_portion,(long)frac_portion);
}