From 26e85736a52f5dd6cf2395c06a151d17ae0512f1 Mon Sep 17 00:00:00 2001
From: Dennis Mannhart <dennis.mannhart@gmail.com>
Date: Fri, 28 Apr 2017 17:29:34 +0200
Subject: [PATCH] land_detector: Reduce and detection false negatives due to
 estimator bias

Using the vertical derivative estimate prevents vertical velocity offsets caused by estimation vertical velocity errors preventing the vehicle disarming.
---
 src/modules/land_detector/MulticopterLandDetector.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/modules/land_detector/MulticopterLandDetector.cpp b/src/modules/land_detector/MulticopterLandDetector.cpp
index ab14652395..40de5fc614 100644
--- a/src/modules/land_detector/MulticopterLandDetector.cpp
+++ b/src/modules/land_detector/MulticopterLandDetector.cpp
@@ -197,7 +197,7 @@ bool MulticopterLandDetector::_get_ground_contact_state()
 		// Adjust maxClimbRate if land_speed is lower than 2x maxClimbrate
 		float maxClimbRate = ((land_speed_threshold * 0.5f) < _params.maxClimbRate) ? (0.5f * land_speed_threshold) :
 				     _params.maxClimbRate;
-		verticalMovement = fabsf(_vehicleLocalPosition.vz) > maxClimbRate;
+		verticalMovement = fabsf(_vehicleLocalPosition.z_deriv) > maxClimbRate;
 	}
 
 	// Check if we are moving horizontally.