fix rangefinder params

ROMFS/px4fmu_common/init.d-posix/airframes/4016_gz_x500_lidar_down

@@ -8,3 +8,6 @@
 PX4_SIM_MODEL=${PX4_SIM_MODEL:=x500_lidar_down}
 
 . ${R}etc/init.d-posix/airframes/4001_gz_x500
+
+param set-default EKF2_RNG_POS_Z -0.177
+param set-default EKF2_MIN_RNG 0

src/modules/ekf2/params_range_finder.yaml

@@ -119,7 +119,7 @@ parameters:
     EKF2_RNG_POS_X:
       description:
         short: X position of range finder origin in body frame
-        long: Forward axis with origin relative to vehicle centre of gravity
+        long: Forward axis (roll) with origin relative to vehicle centre of gravity
       type: float
       default: 0.0
       unit: m
@@ -127,7 +127,7 @@ parameters:
     EKF2_RNG_POS_Y:
       description:
         short: Y position of range finder origin in body frame
-        long: Forward axis with origin relative to vehicle centre of gravity
+        long: Right axis (pitch) with origin relative to vehicle centre of gravity
       type: float
       default: 0.0
       unit: m
@@ -135,7 +135,7 @@ parameters:
     EKF2_RNG_POS_Z:
       description:
         short: Z position of range finder origin in body frame
-        long: Forward axis with origin relative to vehicle centre of gravity
+        long: Down axis (yaw) with origin relative to vehicle centre of gravity
       type: float
       default: 0.0
       unit: m

src/modules/ekf2/params_terrain.yaml

@@ -28,7 +28,7 @@ parameters:
           where the range finder may be inside its minimum measurements distance when
           on ground.
       type: float
-      default: 0.1
+      default: 0
-      min: 0.01
+      min: 0
       unit: m
       decimal: 2