add obstacle_distance message

msg/obstacle_distance.msg

@@ -0,0 +1,14 @@
+# Obstacle distances in front of the sensor.
+
+uint8 sensor_type # Type from MAV_DISTANCE_SENSOR enum.
+uint8 MAV_DISTANCE_SENSOR_LASER = 0
+uint8 MAV_DISTANCE_SENSOR_ULTRASOUND = 1
+uint8 MAV_DISTANCE_SENSOR_INFRARED = 2
+uint8 MAV_DISTANCE_SENSOR_RADAR = 3
+
+uint16[72] distances # Distance of obstacles in front of the sensor starting on the left side. A value of 0 means that the obstacle is right in front of the sensor. A value of max_distance +1 means no obstace is present. A value of UINT16_MAX for unknown/not used. In a array element, each unit corresponds to 1cm.
+
+uint8 increment # Angular width in degrees of each array element.
+
+uint16 min_distance # Minimum distance the sensor can measure in centimeters.
+uint16 max_distance # Maximum distance the sensor can measure in centimeters.