Altitudes in Mission Planner and in Automatic Flight Mode

Hi all,

I’m getting a bit confused about the different altitude parameters shown in Mission Planner. First, there is the altasl parameter, which seems to be the GPS altitude. Second, there is the alt parameter which seems to be the barometer altitude (is it?). But how is the alt_error calculated and which altitude is used for automatic flying modes, like Guided or Alt Hold? For example, when I’m taking off or flying to a point with 5m height, is this GPS or barometer height, if both are different?

I hope someone can clarify this.
Thanks in advance,