Terrain Following Using SRTM Method

The terrain following feature is supported by the Arducopter ecosystem, which the X55 is using. However, this feature has not been heavily tested by our engineering team, so we do not recommend using it unless absolutely necessary, and using this feature is not covered under our standard warranty, so you may use it at your own risk.

The accuracy of the SRTM database varies over the surface of the earth. Typical accuracy is around 10m but inaccuracy of 35m has been detected. This makes terrain following suitable only for altitudes of 60 meters or more.

The X55 supports terrain following using SRTM features in auto flight mode (Auto, RTL and LAND). This feature allows the X55 to climb or descend to maintain a specified distance above the terrain when flying in these modes.

Source of Terrain data

We recommend downloading a set of terrain data tiles for any anticipated flight area using this web utility (Link:https://terrain.ardupilot.org/)

It will create tiles for the specified radius around a geographic location. Then you can download them, unzip and write in the APM/TERRAIN folder of the SD card. Please refer to Advanced Section > Flight Log on how to remove the SD card from the flight controller.

To set up the terrain following feature

• Set TERRAIN_ENABLE to 1

• Using a recent version of Mission Planner (or other GCS that supports terrain following) on the Flight Plan screen, set the altitude type to “Terrain”. Once set all mission commands that include an “Alt” field will be interpreted as altitudes-above-terrain.

When planning missions containing commands with different altitudes-above-terrain keep in mind that the vehicle’s altitude-above-terrain will gradually change between the waypoints. I.e. it will not immediately climb or descend to the new target altitude-above-terrain as it starts towards the next waypoint. In practice it is best to set the initial take-off command’s altitude high enough to clear obstacles.

• Upload the mission to the vehicle and execute the mission as you normally would in AUTO

Using Terrain Altitude during RTL and Land

In some situations, an operator might want the X55 to climb over hills on its return path to home. This can be achieved by using terrain altitude during RLT or land. We generally do not recommend using it unless absolutely necessary. To activate this feature, do the following:

• Set the TERRAIN_ENABLE parameter to 1 to enable using terrain data in RTL and Land flight modes.

• Set RTL_ALT_TYPE to 1 (terrain) and then set WPNAV_RFND_USE=0 to use the Terrain database.