AP_Scripting: added example sending ADSB_VEHICLE

this is a useful example showing how to display an ADSB icon on the
GCS from lua. It also shows how to send mavlink messages with
string.pack()

Author: tridge

libraries/AP_Scripting/examples/adsb_send.lua

@@ -0,0 +1,134 @@
+--[[
+    adsb_send.lua: send a simulated ADSB vehicle flying a 500m radius circle
+
+    This script demonstrates how to send ADSB_VEHICLE MAVLink messages using
+    -- mavlink:send_chan() with manual struct packing (no MAVLink module required)
+--]]
+
+-- initialise mavlink (no rx needed, only tx)
+mavlink:init(1, 0)
+
+local ADSB_VEHICLE_MSGID = 246
+
+-- ADSB flags bitmask values
+local ADSB_FLAGS_VALID_COORDS              = 1
+local ADSB_FLAGS_VALID_ALTITUDE            = 2
+local ADSB_FLAGS_VALID_HEADING             = 4
+local ADSB_FLAGS_VALID_VELOCITY            = 8
+local ADSB_FLAGS_VALID_CALLSIGN            = 16
+local ADSB_FLAGS_SIMULATED                 = 64
+local ADSB_FLAGS_VERTICAL_VELOCITY_VALID   = 128
+
+--
+-- Send an ADSB_VEHICLE message on all MAVLink channels
+--
+-- lat_deg      : latitude in degrees
+-- lng_deg      : longitude in degrees
+-- alt_amsl_m   : altitude AMSL in metres
+-- heading_deg  : course over ground in degrees (0=north, clockwise)
+-- speed_mps    : horizontal speed in m/s
+-- vspeed_mps   : vertical speed in m/s (positive = up)
+-- icao_address : 24-bit ICAO address
+-- callsign     : up to 8 character string
+-- squawk       : squawk code in decimal (e.g. 1200 for VFR)
+-- emitter_type : ADSB_EMITTER_TYPE enum value
+-- flags        : ADSB_FLAGS bitmask
+--
+local function send_ADSB_VEHICLE(lat_deg, lng_deg, alt_amsl_m, heading_deg,
+                                 speed_mps, vspeed_mps, icao_address,
+                                 callsign, squawk, emitter_type, flags)
+    -- pad or truncate callsign to exactly 9 bytes (8 chars + null)
+    local cs = callsign .. string.rep("\0", 9)
+    cs = string.sub(cs, 1, 9)
+
+    -- MAVLink wire order: fields sorted by type size descending, then XML order
+    --   uint32: ICAO_address, lat, lon, altitude          (4 x I4/i4)
+    --   uint16: heading, hor_velocity, ver_velocity,      (5 x I2/i2)
+    --           flags, squawk
+    --   uint8:  altitude_type                             (1 x B)
+    --   char[9]: callsign                                 (c9)
+    --   uint8:  emitter_type, tslc                        (2 x B)
+    local payload = string.pack("<I4i4i4i4 I2I2i2I2I2 Bc9BB",
+        icao_address,
+        math.floor(lat_deg * 1e7),          -- degE7
+        math.floor(lng_deg * 1e7),          -- degE7
+        math.floor(alt_amsl_m * 1000),      -- mm
+        math.floor(heading_deg * 100),      -- cdeg
+        math.floor(speed_mps * 100),        -- cm/s
+        math.floor(vspeed_mps * 100),       -- cm/s
+        flags,
+        squawk,
+        0,                                  -- altitude_type: PRESSURE_QNH
+        cs,
+        emitter_type,
+        0)                                  -- tslc
+
+    for chan = 0, 5 do
+        mavlink:send_chan(chan, ADSB_VEHICLE_MSGID, payload)
+    end
+end
+
+-- circle parameters
+local RADIUS_M   = 500       -- circle radius in metres
+local ALT_AMSL_M = 100       -- altitude AMSL in metres
+local SPEED_MPS  = 50         -- ground speed in m/s
+local ICAO_ADDR  = 0xFABCDE  -- fake ICAO address (0xF00000-0xFFFFFF is unallocated)
+local CALLSIGN   = "SIM12345"
+local UPDATE_HZ  = 5          -- send rate
+
+local FLAGS = ADSB_FLAGS_VALID_COORDS + ADSB_FLAGS_VALID_ALTITUDE
+            + ADSB_FLAGS_VALID_HEADING + ADSB_FLAGS_VALID_VELOCITY
+            + ADSB_FLAGS_VALID_CALLSIGN + ADSB_FLAGS_SIMULATED
+            + ADSB_FLAGS_VERTICAL_VELOCITY_VALID
+
+-- angular rate in rad/s
+local OMEGA = SPEED_MPS / RADIUS_M
+local angle_rad = 0
+
+local function update()
+    local home = ahrs:get_home()
+    if not home then
+        return update, 1000
+    end
+
+    local center_lat = home:lat()
+    local center_lng = home:lng()
+    local alt_m = ALT_AMSL_M + home:alt()*0.01
+
+    local dt = 1.0 / UPDATE_HZ
+    angle_rad = angle_rad + OMEGA * dt
+    if angle_rad > 2 * math.pi then
+        angle_rad = angle_rad - 2 * math.pi
+    end
+
+    -- compute position on circle
+    local pos = Location()
+    pos:lat(center_lat)
+    pos:lng(center_lng)
+    pos:alt(math.floor(alt_m * 100))
+    pos:offset_bearing(math.deg(angle_rad), RADIUS_M)
+
+    -- heading is tangent to circle (90 degrees ahead of radial)
+    local heading_deg = math.deg(angle_rad) + 90
+    if heading_deg >= 360 then
+        heading_deg = heading_deg - 360
+    end
+
+    send_ADSB_VEHICLE(
+        pos:lat() / 1e7,    -- back to degrees
+        pos:lng() / 1e7,    -- back to degrees
+        alt_m,
+        heading_deg,
+        SPEED_MPS,
+        0,                  -- no vertical speed
+        ICAO_ADDR,
+        CALLSIGN,
+        1200,               -- VFR squawk
+        1,                  -- ADSB_EMITTER_TYPE_LIGHT
+        FLAGS
+    )
+
+    return update, math.floor(1000 / UPDATE_HZ)
+end
+
+return update()