Terrain follow

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Supported for: Ardupilot only.
1. If a vehicle is equipped with altimeter then in the AGL field of Telemetry Card the Client will display values from the altimeter, otherwise values, calculated by Server. Client determines from telemetry field altitude_agl, received from S_FLIGHT_CONTROLLER subsystem, if the drone has an altimeter or not.
2. Each route segment contains Altitude mode attribute. Select one of following values:
• AMSL - available for all platforms;
• AGL - available for all platforms;
• Range Finder - available for Ardupilot platform only.
Last selected value is used when new segment is created. If last used value is not supported by the current platform or there is no last used value then AGL is used.
3. Safe distance over terrain parameter is ignored during route calculation for segments with Range Finder altitude mode.
4. The drone follows terrain with altimeter between the segment with Range Finder altitude mode to the next segment. If the segment itself contains flight path (like area scan) the drone will also fly this path using an altimeter to keep height over terrain.

Terrain follow.png

5. To keep safe entrance in low height segments (height < safe height over terrain), ucs requires it to be preceded by a segment with Range Finder altitude mode and on the safe altitude (height >= safe height over terrain). This restriction is required by the following example. The route consists of two segments:
- Waipoint: height = 10m, altitude mode = AGL.
- Areascan: height = 1m, altitude mode = rangefinder. The vehicle moves from the waypoint to the first the point of area scan without altimeter. It will start using altimeter only when it reaches the first point of area scan. If GPS or elevation data is not accurate enough then the vehicle will crash.
6. Calculated flight path for Range Finder segments drawing features:
6.1. It has a specific color to highlight such segments.
6.2. Server resolves flight path with as few points as possible, Client inserts intermediate invisible points into the displayed flight path to make it close to terrain landscape.

7. If the uploaded route contains at least one Range Finder segment, VSM checks if the vehicle supports Terrain Follow Mode or not.
7.a. If the vehicle doesn’t support Terrain Follow Mode, VSM shows an error.
7.b. Otherwise VSM sets up autopilot properly. Switch the vehicle in auto mode and the vehicle flies along the route. While flying Range Finder section the vehicle keeps the same height from terrain, regardless of obstacles.
8. When a mission is paused on location WPP and then continued, the vehicle gets to WPP on the safe altitude (safe height over terrain in vehicle profile), then it gets WPP’s altitude and continues route just as if it had flown the entire route.

Note: See rangefinder’s manual to set the correct maximum rangefinder altitude in “Vehicle profile section”

Max rangefinder alt.png