Mavros setpoint_position/global not working

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Hello everyone,

I'm trying to use mavros with rospy in order to make my drone takeoff and go to some waypoints. Right now I'm running my experiments in STIL, not a real drone.

However, I can't manage to make the drone move to the desired waypoint. I'm trying to use the topic '/mavros/setpoint_position/global' to publish the coordinates, like this:

setpoint_global_pub = rospy.Publisher(
            '/mavros/setpoint_position/global',
            mavros_msgs.msg.GlobalPositionTarget,
            queue_size=1,
            latch=True)

setpoint_global_pub.publish(latitude= -27.603683, longitude= -48.518052, altitude=40)

I get this message in mavros:

 [WARN] [1553207581.536736778]: SPG: sp not sent.

Any suggestions?

Btw I'm setting the mode to GUIDED and taking off first