ardupilot/libraries/AP_Math/location.cpp

143 lines
4.9 KiB
C++

/// -*- 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 <http://www.gnu.org/licenses/>.
*/
/*
* this module deals with calculations involving struct Location
*/
#include <stdlib.h>
#include "AP_Math.h"
// radius of earth in meters
#define RADIUS_OF_EARTH 6378100
static 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((fabsf((float)loc->lat)/1.0e7f) * 0.0174532925f);
last_lat = loc->lat;
return scale;
}
// return distance in meters to 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) * 0.01113195f;
}
// 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(struct Location &location,
struct Location &point1,
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
* thanks to http://www.movable-type.co.uk/scripts/latlong.html
*
* This function is precise, but costs about 1.7 milliseconds on an AVR2560
*/
void location_update(struct Location *loc, float bearing, float distance)
{
float lat1 = radians(loc->lat*1.0e-7f);
float lon1 = radians(loc->lng*1.0e-7f);
float brng = radians(bearing);
float dr = distance/RADIUS_OF_EARTH;
float lat2 = asinf(sinf(lat1)*cosf(dr) +
cosf(lat1)*sinf(dr)*cosf(brng));
float lon2 = lon1 + atan2f(sinf(brng)*sinf(dr)*cosf(lat1),
cosf(dr)-sinf(lat1)*sinf(lat2));
loc->lat = degrees(lat2)*1.0e7f;
loc->lng = degrees(lon2)*1.0e7f;
}
/*
* 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) {
float dlat = ofs_north * 89.831520982f;
float dlng = (ofs_east * 89.831520982f) / longitude_scale(loc);
loc->lat += dlat;
loc->lng += dlng;
}
}