SITL: created ADSB simulator to generate additional ghost aircraft within SITL

The values are very aggressive, you'll come into contact with another aircraft very soon
Credit goes to Tridge for this work

This feature is enabled with the following command:
sim_vehicle -A --adsb

libraries/SITL/SIM_ADSB.cpp

@@ -0,0 +1,205 @@
+/// -*- 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/>.
+ */
+/*
+  ADSB simulator class for MAVLink ADSB peripheral
+*/
+
+#include "SIM_ADSB.h"
+
+#include <stdio.h>
+
+#include "SIM_Aircraft.h"
+
+namespace SITL {
+
+ADSB::ADSB(const struct sitl_fdm &_fdm, const char *_home_str) :
+    fdm(_fdm)
+{
+    float yaw_degrees;
+    Aircraft::parse_home(_home_str, home, yaw_degrees);
+}
+
+
+/*
+  update a simulated vehicle
+ */
+void ADSB_Vehicle::update(float delta_t)
+{
+    if (!initialised) {
+        initialised = true;
+        ICAO_address = (uint32_t)(rand() % 10000);
+        snprintf(callsign, sizeof(callsign), "SIM%u", ICAO_address);
+        position.x = Aircraft::rand_normal(0, 1000);
+        position.y = Aircraft::rand_normal(0, 1000);
+        position.z = -fabsf(Aircraft::rand_normal(3000, 1000));
+        velocity_ef.x = Aircraft::rand_normal(5, 20);
+        velocity_ef.y = Aircraft::rand_normal(5, 20);
+        velocity_ef.z = Aircraft::rand_normal(0, 3);
+    }
+
+    position += velocity_ef * delta_t;
+    if (position.z > 0) {
+        // it has crashed! reset
+        initialised = false;
+    }
+}
+
+/*
+  update the ADSB peripheral state
+*/
+void ADSB::update(void)
+{
+    // calculate delta time in seconds
+    uint32_t now_us = AP_HAL::micros();
+
+    float delta_t = (now_us - last_update_us) * 1.0e-6f;
+    last_update_us = now_us;
+
+    for (uint8_t i=0; i<num_vehicles; i++) {
+        vehicles[i].update(delta_t);
+    }
+    
+    // see if we should do a report
+    send_report();
+}
+
+/*
+  send a report to the vehicle control code over MAVLink
+*/
+void ADSB::send_report(void)
+{
+    if (!mavlink.connected && mav_socket.connect(target_address, target_port)) {
+        ::printf("ADSB connected to %s:%u\n", target_address, (unsigned)target_port);
+        mavlink.connected = true;
+    }
+    if (!mavlink.connected) {
+        return;
+    }
+
+    // check for incoming MAVLink messages
+    uint8_t buf[100];
+    ssize_t ret;
+
+    while ((ret=mav_socket.recv(buf, sizeof(buf), 0)) > 0) {
+        for (uint8_t i=0; i<ret; i++) {
+            mavlink_message_t msg;
+            mavlink_status_t status;
+            if (mavlink_frame_char_buffer(&mavlink.rxmsg, &mavlink.status,
+                                          buf[i],
+                                          &msg, &status) == MAVLINK_FRAMING_OK) {
+                switch (msg.msgid) {
+                case MAVLINK_MSG_ID_HEARTBEAT: {
+                    if (!seen_heartbeat) {
+                        seen_heartbeat = true;
+                        vehicle_component_id = msg.compid;
+                        vehicle_system_id = msg.sysid;
+                        ::printf("ADSB using srcSystem %u\n", (unsigned)vehicle_system_id);
+                    }
+                    break;
+                }
+                }
+            }
+        }
+    }
+
+    if (!seen_heartbeat) {
+        return;
+    }
+
+    uint32_t now = AP_HAL::millis();
+    mavlink_message_t msg;
+    uint16_t len;
+
+    if (now - last_heartbeat_ms >= 1000) {
+        mavlink_heartbeat_t heartbeat;
+        heartbeat.type = MAV_TYPE_ADSB;
+        heartbeat.autopilot = MAV_AUTOPILOT_ARDUPILOTMEGA;
+        heartbeat.base_mode = 0;
+        heartbeat.system_status = 0;
+        heartbeat.mavlink_version = 0;
+        heartbeat.custom_mode = 0;
+
+        /*
+          save and restore sequence number for chan0, as it is used by
+          generated encode functions
+         */
+        mavlink_status_t *chan0_status = mavlink_get_channel_status(MAVLINK_COMM_0);
+        uint8_t saved_seq = chan0_status->current_tx_seq;
+        chan0_status->current_tx_seq = mavlink.seq;
+        len = mavlink_msg_heartbeat_encode(vehicle_system_id,
+                                           vehicle_component_id,
+                                           &msg, &heartbeat);
+        chan0_status->current_tx_seq = saved_seq;
+
+        mav_socket.send(&msg.magic, len);
+
+        last_heartbeat_ms = now;
+    }
+
+
+    /*
+      send a ADSB_VEHICLE messages
+     */
+    uint32_t now_us = AP_HAL::micros();
+    if (now_us - last_report_us > reporting_period_ms*1000UL) {
+        for (uint8_t i=0; i<num_vehicles; i++) {
+            ADSB_Vehicle &vehicle = vehicles[i];
+            Location loc = home;
+
+            location_offset(loc, vehicle.position.x, vehicle.position.y);
+
+            // re-init when over 50km from home
+            if (get_distance(home, loc) > 1000) {
+                vehicle.initialised = false;
+            }
+            
+            mavlink_adsb_vehicle_t adsb_vehicle {};
+            last_report_us = now_us;
+
+            adsb_vehicle.ICAO_address = vehicle.ICAO_address;
+            adsb_vehicle.lat = loc.lat*1.0e-7f;
+            adsb_vehicle.lon = loc.lng*1.0e-7f;
+            adsb_vehicle.altitude_type = ADSB_ALTITUDE_TYPE_PRESSURE_QNH;
+            adsb_vehicle.altitude = -vehicle.position.z;
+            adsb_vehicle.heading = wrap_360_cd(100*degrees(atan2f(vehicle.velocity_ef.y, vehicle.velocity_ef.x))) / 100;
+            adsb_vehicle.hor_velocity = pythagorous2(vehicle.velocity_ef.x, vehicle.velocity_ef.y);
+            adsb_vehicle.ver_velocity = -vehicle.velocity_ef.z;
+            memcpy(adsb_vehicle.callsign, vehicle.callsign, sizeof(adsb_vehicle.callsign));
+            adsb_vehicle.emitter_type = ADSB_EMITTER_TYPE_LARGE;
+            adsb_vehicle.tslc = 1;
+            adsb_vehicle.flags =
+                ADSB_FLAGS_VALID_COORDS |
+                ADSB_FLAGS_VALID_ALTITUDE |
+                ADSB_FLAGS_VALID_HEADING |
+                ADSB_FLAGS_VALID_VELOCITY |
+                ADSB_FLAGS_VALID_CALLSIGN |
+                ADSB_FLAGS_SIMULATED;
+
+            mavlink_status_t *chan0_status = mavlink_get_channel_status(MAVLINK_COMM_0);
+            uint8_t saved_seq = chan0_status->current_tx_seq;
+            chan0_status->current_tx_seq = mavlink.seq;
+            len = mavlink_msg_adsb_vehicle_encode(vehicle_system_id,
+                                                  MAV_COMP_ID_ADSB,
+                                                  &msg, &adsb_vehicle);
+            chan0_status->current_tx_seq = saved_seq;
+            
+            mav_socket.send(&msg.magic, len);
+        }
+    }
+    
+}
+
+} // namespace SITL

libraries/SITL/SIM_ADSB.h

@@ -0,0 +1,80 @@
+/// -*- 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/>.
+ */
+/*
+  ADSB peripheral simulator class
+*/
+
+#pragma once
+
+#include <AP_HAL/utility/Socket.h>
+
+#include "SIM_Aircraft.h"
+
+namespace SITL {
+
+/*
+  a class for individual simulated vehicles
+*/
+class ADSB_Vehicle {
+    friend class ADSB;
+
+private:
+    void update(float delta_t);
+    
+    Vector3f position; // NED from origin
+    Vector3f velocity_ef; // NED
+    char callsign[9];
+    uint32_t ICAO_address;
+    bool initialised = false;
+};
+        
+class ADSB {
+public:
+    ADSB(const struct sitl_fdm &_fdm, const char *home_str);
+    void update(void);
+
+private:
+    const struct sitl_fdm &fdm;
+    const char *target_address = "127.0.0.1";
+    const uint16_t target_port = 5762;
+
+    Location home;
+    static const uint8_t num_vehicles = 6;
+    ADSB_Vehicle vehicles[num_vehicles];
+    
+    // reporting period in ms
+    const float reporting_period_ms = 500;
+    uint32_t last_report_us = 0;
+    uint32_t last_update_us = 0;
+    
+    uint32_t last_heartbeat_ms = 0;
+    bool seen_heartbeat = false;
+    uint8_t vehicle_system_id;
+    uint8_t vehicle_component_id;
+
+    SocketAPM mav_socket { false };
+    struct {
+        // socket to telem2 on aircraft
+        bool connected;
+        mavlink_message_t rxmsg;
+        mavlink_status_t status;
+        uint8_t seq;
+    } mavlink {};
+
+    void send_report(void);
+};
+
+}  // namespace SITL

libraries/SITL/SIM_Aircraft.cpp

@@ -55,22 +55,13 @@ Aircraft::Aircraft(const char *home_str, const char *frame_str) :
     min_sleep_time(5000)
 #endif
 {
-    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);
+    float yaw_degrees;
 
-    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;
+    parse_home(home_str, home, yaw_degrees);
     location = home;
     ground_level = home.alt*0.01;
 
-    dcm.from_euler(0, 0, radians(atof(yaw_s)));
-    free(s);
+    dcm.from_euler(0, 0, radians(yaw_degrees));
 
     set_speedup(1);
 
@@ -78,6 +69,45 @@ Aircraft::Aircraft(const char *home_str, const char *frame_str) :
     frame_counter = 0;
 }
 
+
+/*
+  parse a home string into a location and yaw
+ */
+bool Aircraft::parse_home(const char *home_str, Location &loc, float &yaw_degrees)
+{
+    char *saveptr=NULL;
+    char *s = strdup(home_str);
+    if (!s) {
+        return false;
+    }
+    char *lat_s = strtok_r(s, ",", &saveptr);
+    if (!lat_s) {
+        return false;
+    }
+    char *lon_s = strtok_r(NULL, ",", &saveptr);
+    if (!lon_s) {
+        return false;
+    }
+    char *alt_s = strtok_r(NULL, ",", &saveptr);
+    if (!alt_s) {
+        return false;
+    }
+    char *yaw_s = strtok_r(NULL, ",", &saveptr);
+    if (!yaw_s) {
+        return false;
+    }
+
+    memset(&loc, 0, sizeof(loc));
+    loc.lat = atof(lat_s) * 1.0e7;
+    loc.lng = atof(lon_s) * 1.0e7;
+    loc.alt = atof(alt_s) * 1.0e2;
+
+    yaw_degrees = atof(yaw_s);
+    free(s);
+
+    return true;
+}
+    
 /*
    return true if we are on the ground
 */

libraries/SITL/SIM_Aircraft.h

@@ -72,6 +72,12 @@ public:
     /* fill a sitl_fdm structure from the simulator state */
     void fill_fdm(struct sitl_fdm &fdm) const;
 
+    /* return normal distribution random numbers */
+    static double rand_normal(double mean, double stddev);
+
+    /* parse a home location string */
+    static bool parse_home(const char *home_str, Location &loc, float &yaw_degrees);
+
     // get frame rate of model in Hz
     float get_rate_hz(void) const { return rate_hz; }       
     
@@ -134,9 +140,6 @@ protected:
     /* return wall clock time in microseconds since 1970 */
     uint64_t get_wall_time_us(void) const;
 
-    /* return normal distribution random numbers */
-    double rand_normal(double mean, double stddev);
-
 private:
     uint64_t last_time_us = 0;
     uint32_t frame_counter = 0;