Mission Continuation & Terrain Following Updates - 3.1 Software Release

New Features Available!

We've recently started using the new release of QGroundControl for the hand controller and computer. In order to fully utilize the new features included with that release, we have updated Discovery's onboard software. Now you can use Terrain Following and Mission Continuation to improve your workflow and increase data collection efficiency.

Terrain Following

Terrain Following is...

Terrain following refers to the ability of an aircraft to maintain a relatively constant altitude above ground level. When you use terrain following for a flight mission, the software will utilize elevation data to calculate flight altitude, rather than using one set altitude based on the launch position. 

Terrain Following is not...

Terrain following is not a substitute or alternative for obstacle avoidance, and it is not to be used as a replacement for the Pilot-in-Command or Visual Observers. ALWAYS follow FAA Guidelines.

Terrain data is based on GROUND ELEVATION

The drone will not see or climb over trees or other obstacles

Using Terrain Following... 

Using this feature is beneficial in areas with significant terrain variation such as large rolling hills, mountains, cliffs, etc.

Using Terrain Following can help you achieve consistent LiDAR point density and camera GSD throughout a jobsight. 

LiDAR Range

LiDAR sensors have a specified max range (distance from sensor to target) at which they can sufficiently capture a ground point. Therefore, it's important not to fly the drone at an altitude greater than that max.

Discovery 2 - Max distance from sensor to ground = 60 meters

Discovery 3 - Max distance from sensor to ground = 90 meters

Camera Range

If you are going to produce an orthomosaic for the job, you will want to set your flight altitude to meet your camera GSD requirements. Use the formulas below to determine the flight altitude you will need to set in order to achieve your required GSD. 

Estimated GSD (cm/pixel) = Altitude x 0.02875

Estimated GSD (in/pixel) = Altitude x 0.0113

Lastly, consider the optimal photogrammetry range. Photogrammetry performs best when images can capture variations. These variations are used to align the images to create an orthomosaic.

If you are too close to objects that have very little variation (ie. dense forest or plain desert), your processing software may have difficulty understanding how to knit images together.

Maintain Distance Between Sensors & Ground

Now that you have determined your optimal altitude for the jobsite, you can use terrain following to set the drone to follow the curvature of the terrain, so you can maintain the distance from the sensors to the ground. The images below illustrate how terrain following solves issues related to sensor proximity to scanned objects.

Precautions for Using Terrain Following

Terrain data is not 100% accurate: The data comes from an array of sources, some of the sources may not be completely up-to-date, and some sources have a broad resolution of 100 meters. Therefore, the terrain at your jobsite can vary from what your drone is programmed to follow. 

Your drone will not follow terrain on RTL: If the drone is below the set altitude relative to its launch, it will climb to reach that altitude before returning to its launch point. If it's above the set altitude, it will maintain its current altitude while returning to the launch point.

Plan Terrain Following Missions Efficiently

Follow Terrain Contour: Any time the drone climbs or descends, it consumes battery power at a faster rate than when it is simply maintaining altitude. For this reason, if your site has mostly flat terrain, you can continue to fly with a fixed altitude for maximum efficiency. 

When you opt to use terrain following, planning along the terrain contour rather than against it will result in more efficient use of battery resources by reducing climbs and descents. 

Set the Following Tolerance: Setting the tolerance makes terrain following flights more efficient. The drone will only climb or descend if the change in terrain altitude is more than the tolerance. 

This can reduce climbs and descents, therefore reducing battery consumption. Consider that this will affect your sensor distance to ground.

ALWAYS set the tolerance to 3m!
Leaving tolerance at 0m can cause excessive battery consumption

Download Map Tiles with an Internet Connection: Be sure to download map tiles and "Fetch Elevation Data" while connected to internet. This elevation data is necessary for terrain following, and may not be accessible if you don't have a WiFi signal available.

1. Plan the mission as before setting your altitude and path
2. Once complete, with the path click the "Terrain" tab (mountains icon)
3. Click the dropdown to select the "Altitude Mode"
4. Select "Calculated Above Terrain"
5. Set the tolerance to 3 meters
6. Review the bottom of the screen to ensure that the orange flight line stays comfortably above the green terrain line
7. During upload of the mission, you may see additional waypoints used to adjust altitude above terrain by specifying climbs and descents

Terrain Following lesson complete! Now let's talk about Mission Continuation...