Copter: landing gear deployment height calc uses lidar status

ArduCopter/landing_gear.cpp

@@ -29,12 +29,26 @@ void Copter::landinggear_update()
 
     last_deploy_status = landinggear.deployed();
 
-    // support height based triggering
-    float height;
-    if (rangefinder_alt_ok()) {
+    // support height based triggering using rangefinder or altitude above home
+    float height = current_loc.alt * 0.01;
+
+    // use rangefinder if available
+    switch (rangefinder.status_orient(ROTATION_PITCH_270)) {
+    case RangeFinder::RangeFinder_NotConnected:
+    case RangeFinder::RangeFinder_NoData:
+        // use altitude above home for non-functioning rangefinder
+        break;
+
+    case RangeFinder::RangeFinder_OutOfRangeLow:
+        // altitude is close to zero (gear should deploy)
+        height = 0.0f;
+        break;
+
+    case RangeFinder::RangeFinder_OutOfRangeHigh:
+    case RangeFinder::RangeFinder_Good:
+        // use last good reading
         height = rangefinder_state.alt_cm_filt.get() * 0.01;
-    } else {
-        height = current_loc.alt * 0.01;
+        break;
     }
 
     landinggear.update(height);