Line of Sight in Drone Flight Patterns

Line of Sight (LOS) analysis is critical for effective drone operations, particularly when capturing imagery for inspection or mapping. Building on our knowledge hub article: Mapping the Skies: The Science of Survey Patterns, this technical deep-dive examines how Carmenta Engine’s line-of-sight capabilities enhance flight pattern generation for uncrewed aerial systems.

While our previous exploration covered pattern types and terrain challenges, here we focus specifically on the visibility analysis to ensure that each waypoint is correctly placed and allows to capture usable data.

The Line-of-Sight Challenge

When planning drone surveys, ensuring the camera has an unobstructed view of target areas is essential. Obstacles, terrain variations, and structures can block visibility, leading to incomplete or unusable data. Traditional flight planning without LOS verification often results in:

• Data gaps requiring costly re-flights
• Wasted time capturing obstructed views
• Inconsistent image quality across the survey area

Technical Implementation with Carmenta Engine

The LineOfSightOperator in Carmenta Engine provides comprehensive visibility analysis that can be integrated into flight pattern generation. This operator calculates viewsheds from specified observer points, determining what areas are visible from each position.

Example: Basic Line of Sight Setup

public static LineOfSightOperator CreateDronePatternLosOperator(Operator elevationInput, Point dronePositionWgs84LatLong) 
{
   // Create a new LineOfSightOperator
   LineOfSightOperator losOperator = new();

   // Set the elevation input in the LineOfSightOperator
   losOperator.ElevationInput = elevationInput;

   // Create a MemoryDataSet for the drone observer position
   MemoryDataSet observerDataSet = new MemoryDataSet(Crs.Wgs84LongLat);

   // Add the MemoryDataSet as ObserverInput to the LineOfSightOperator
   losOperator.ObserverInput = new ReadOperator(observerDataSet);

   // Create a point Feature at the drone's position
   Feature observerFeature = new Feature(
   new PointGeometry(dronePositionWgs84LatLong), Crs.Wgs84LongLat);

   // Add the observer feature to the MemoryDataSet
   observerDataSet.Insert(observerFeature);

   // Configure for airborne drone operations
   losOperator.CarrierType = CarrierType.Airborne;

   // Set camera field of view parameters (typical for survey drones)
   losOperator.PictureWidth = 80.0; // Horizontal FOV in degrees
   losOperator.PictureHeight = 60.0; // Vertical FOV in degrees
   losOperator.PictureElevation = -90.0; // Nadir view for mapping (straight down)

   // Configure height references for drone operations
   losOperator.ObserverHeightType = HeightType.AboveGround;
   losOperator.MinVisibilityHeightType = HeightType.AboveGround;

   // Set the effective range based on camera capabilities
   losOperator.MaxDistance = 100.0; // 100m effective range for detailed inspection
   losOperator.MaxDistanceType = DistanceType.ThreeDimensional;

   // Enable outputting visibility heights to determine if targets are visible
   losOperator.OutputMinVisibilityHeights = true;

   return losOperator;
}

Integration with Pattern Generation

When generating flight patterns, LineOfSightOperator can be used to:

1. Validate waypoints: Verify each generated waypoint has a clear view of its target
2. Optimize camera angles: Adjust pitch and bearing for best visibility
3. Identify coverage gaps: Find areas requiring additional viewpoints

For example, in an infrastructure inspection pattern:

// Pattern generation with LOS integration
PointCollection patternPoints = new();
MemoryDataSet observerDataSet = new MemoryDataSet(Crs.Wgs84LongLat);
LineOfSightOperator losOperator = CreateDronePatternLosOperator(elevationInput, startPosition);
losOperator.ObserverInput = new ReadOperator(observerDataSet);

// For each potential waypoint around a structure
foreach (var position in calculatedPositions) {
    // Clear previous observer points
    observerDataSet.Clear();

    // Calculate direction from drone to target
    double bearing = CalculateBearing(position, target);

    // Update LOS parameters for this position
    losOperator.PictureDirection = bearing;

    // Create and add new observer at this position
    Feature observerFeature = new Feature(new PointGeometry(position), Crs.Wgs84LongLat);
    observerDataSet.Insert(observerFeature);

    // Get visibility analysis result
    Feature visibilityResult = losOperator.GetRasterFeature();
    bool hasLos = DetermineVisibility(visibilityResult, target);

    // Only add waypoints with clear visibility
    if (hasLos) {
        patternPoints.Add(position);
    }
}

Applications in Different Patterns

Different survey patterns benefit from LOS analysis in specific ways, for example,

• Box Pattern for Structure Inspection: for building inspection, LOS verification ensures each face is properly visible,
• Parallel Pattern for Area Coverage: For terrain mapping, LOS analysis helps identify optimal flight heights

Advanced Features

• Tree height consideration: Account for vegetation that may block views using TreeHeightInput property:
  losOperator.TreeHeightInput = treeHeightRasterOperator;
• Refraction modeling: Account for atmospheric effects on visibility using Refraction property:
  losOperator.Refraction = 0.13; // Standard refraction coefficient
• Multiple viewing directions: Check visibility in opposing directions using SecondPictureBackwards property:
  losOperator.SecondPictureBackwards = true; // Look backward as well

Applications for VLOS and BVLOS Operations

VLOS (Visual Line of Sight) Operations

For missions where regulations require the drone to remain within visual line of sight of the operator, LineOfSightOperator can:

1. Plan safe operational boundaries: Calculate the maximum allowable distance based on the operator’s position and height
2. Identify visual obstacles: Map areas where the drone might be visually obscured from the operator
3. Adaptive flight planning: Ensure flight patterns stay within continuously verified VLOS boundaries, especially important in urban or forested environments

BVLOS (Beyond Visual Line of Sight) Operations

For BVLOS operations, which are increasingly permitted with proper risk mitigation, LineOfSightOperator can support:

1. Radio communication reliability: Model line-of-sight between drone and ground control stations
2. Detect-and-Avoid planning: Identify areas with limited visibility where additional caution is needed
3. Emergency landing site identification: Find visible landing locations along routes for contingency planning

LineOfSightOperator thus becomes a critical tool not just for data collection quality but for regulatory compliance and safety in drone operations, enabling increasingly sophisticated missions while maintaining appropriate risk management.

Conclusion

Integrating Carmenta Engine’s LineOfSightOperator into drone flight pattern generation transforms what would otherwise be geometric path planning into terrain-aware, obstacle-avoiding intelligent flight routes. This capability ensures complete coverage, optimal image quality, and efficient flight paths, ultimately delivering more reliable data collection with fewer flights.

As drone regulations evolve to permit more complex operations, particularly in BVLOS scenarios, line-of-sight analysis will become increasingly important not just for data quality but for operational safety and regulatory compliance. The robust visibility modeling provided by tools like LineOfSightOperator will be essential in enabling the next generation of sophisticated drone operations across industries.