Overview

The ALT parameter group contains miscellaneous altitude-related settings.

Note: This group is a bit of a "catch-all" in some documentation sets.

• ALT_OFFSET is a core ArduPlane parameter for adjusting the mission altitude frame.
• ALT_MIN is typically associated with the Proximity library (PRX_ALT_MIN), defining the floor for obstacle avoidance.

Key Concepts

1. Altitude Offset (ALT_OFFSET)

(ArduPlane Only)
This parameter shifts the autopilot's internal reference for "Home Altitude" without actually moving the Home point.

• Usage: Useful for landing at a location that is at a different physical elevation than the takeoff point, or for adjusting altitude during repeated auto-landings in a circuit.
• Math: Target_Alt = Mission_Alt + ALT_OFFSET.

2. Proximity Floor (ALT_MIN)

(From AP_Proximity)
Defines the minimum altitude (AGL) required for the obstacle avoidance system to engage.

• Purpose: Prevents the ground itself from being detected as an "obstacle" during takeoff and landing, which could cause the vehicle to panic or refuse to land.

Parameter Breakdown

• ALT_OFFSET: Altitude offset in meters. Positive adds height to targets.
• ALT_MIN: Minimum altitude for proximity sensors to be active.

Developer Notes

• Context: ALT_OFFSET is defined in ArduPlane/Parameters.cpp. ALT_MIN is defined in libraries/AP_Proximity.