Python Script to send fake GLOBAL_POSITION_INT messages

from time import sleep, time
from pymavlink import mavutil
import math

# Create the connection
connection_one = mavutil.mavlink_connection('udpin:127.0.0.1:14550', source_system=2)
connection_two = mavutil.mavlink_connection('udpin:127.0.0.1:15550', source_system=3)
connection_three = mavutil.mavlink_connection('udpin:127.0.0.1:16550', source_system=4)

# Wait a heartbeat before sending commands
connection_one.wait_heartbeat()
connection_two.wait_heartbeat()
connection_three.wait_heartbeat()

start_time = time()

def time_since_boot_ms():
    return (time() * 1000 - start_time * 1000)

ang_vel = (2 * math.pi / 30) # rad / sec
dt = 1 # sec

start_angle = [0, math.pi / 2, math.pi]
radius = [10000, 8000, 10000]

def xy_on_circle(center, radius, theta_rad):
    x = radius * math.cos(theta_rad)
    y = radius * math.sin(theta_rad)
    x += center[0]
    y += center[1]
    return (x, y)

def theta_now(start_angle, ang_vel):
    return start_angle + (ang_vel * time_since_boot_ms() / 1000)

while True:
    theta = theta_now(start_angle[0], ang_vel) # radians
    center = (-353633600, 1491632350) # lat lon
    latlon = xy_on_circle(center, radius[0], theta)

    connection_one.mav.global_position_int_send(
        int(time_since_boot_ms()),
        int(latlon[0]),
        int(latlon[1]),
        int(684.9 * 1000), # mm alt amsl
        100 * 1000, # relalt mm UP!
        0, # vx
        0, # vy
        0, # vz
        int(math.degrees(theta + (math.pi / 2)) * 100) % (36000)# heading
    )

    theta = theta_now(start_angle[1], ang_vel) # radians
    center = (-353654700, 1491662400) # lat lon
    latlon = xy_on_circle(center, radius[1], theta)
    connection_two.mav.global_position_int_send(
        int(time_since_boot_ms()),
        int(latlon[0]),
        int(latlon[1]),
        int(684.9 * 1000), # mm alt amsl
        100 * 1000, # relalt mm UP!
        0, # vx
        0, # vy
        0, # vz
        int(math.degrees(theta + (math.pi / 2)) * 100) % (36000) # heading
    )

    theta = theta_now(start_angle[2], ang_vel) # radians
    center = (-353602800, 1491661300) # lat lon
    latlon = xy_on_circle(center, radius[2], theta)
    connection_three.mav.global_position_int_send(
        int(time_since_boot_ms()),
        int(latlon[0]),
        int(latlon[1]),
        int(684.9 * 1000), # mm alt amsl
        100 * 1000, # relalt mm UP!
        0, # vx
        0, # vy
        0, # vz
        int(math.degrees(theta + (math.pi / 2)) * 100) % (36000)# heading
    )
    sleep(dt)