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Waterline Calibration

Waterline calibration configures the vertical reference point for range calculations in Lookout+ Nav systems. This user-configurable setting is essential for deployable systems that move between different vessels.

User Configurable

Unlike camera calibration, waterline calibration can be adjusted by users, particularly for deployable equipment (INS, and cameras are in the same unit) that moves between vessels with different mounting configurations.

When Waterline Calibration is Needed​

Deployable Systems​

Systems designed to move between vessels require waterline recalibration:

  • Portable Lookout+ installations
  • Temporary mounting systems
  • Charter or rental vessel operations

Fixed Installations​

Most permanent installations are calibrated once by Greenroom engineers and rarely need adjustment.

Understanding the Transform Tree​

Coordinate System Hierarchy​

Lookout+ uses a transform tree to track relationships between all system components:

Baselink (Reference Point)
├── INS Position
├── Camera Positions
├── Ray Reference
└── Waterline Reference

The baselink serves as the central reference for all measurements:

  • Origin: Usually positioned at the INS location
  • Coordinate System: X (forward), Y (port), Z (up)
  • All Positions: Measured relative to this point
INS and Baselink Relationship

In most installations, the INS position equals the baselink position (INS offsets = 0,0,0). When this is true, the waterline offset represents the height of the INS above the water surface.

Configuration Locations​

GAMA Integrated Systems​

If Lookout+ is integrated with GAMA:

  1. Access GAMA Interface
  2. Navigate to Advanced Settings
  3. Find Vessel Offsets section
  4. Adjust Waterline Z Field

Standalone Lookout+ Systems​

For systems without GAMA integration:

  1. Access Lookout+ Interface at http://localhost:4000/
  2. Navigate to Advanced Settings
  3. Select Sensors section
  4. Find Vessel Offsets
  5. Adjust Waterline Z Field
Vessel offset configuration interface
Vessel offset configuration showing waterline Z-field adjustment

Waterline Configuration Process​

Step 1: Measure Physical Heights​

Accurately measure the vertical distances:

  • INS to Waterline: Vertical distance from INS to water surface
  • Camera to Waterline: Height of cameras above water (if different from INS)
  • Vessel Loading: Consider typical operational loading and speeds. The transform from the waterline -> camera will be used as the camera height

Step 2: Calculate Z Offset​

The waterline Z-field uses a negative value for heights above water:

Formula: Waterline Z = -(Height above water)

Examples:

  • INS 1.68m above waterline → Enter -1.68
  • INS 2.5m above waterline → Enter -2.50
  • INS 0.8m above waterline → Enter -0.80

Step 3: Apply Configuration​

  1. Record Current Values: Note existing settings before changes
  2. Enter New Value: Input calculated waterline Z offset
  3. Verify Settings: Confirm all other offsets remain correct
  4. Test Operation: Verify range measurements appear reasonable
Safety Precautions
  • Backup Current Settings: Always record existing values before making changes
  • Small Adjustments: Make incremental changes when fine-tuning
  • Contact Greenroom: If unsure about any measurements or calculations

Why Waterline vs GPS Altitude​

Tidal Independence​

Using waterline reference instead of GPS altitude provides several advantages:

Waterline Benefits:

  • No Tidal Lookup Required: System works without tide table integration
  • Real-Time Accuracy: Always reflects current water level relationship
  • Simplified Configuration: Direct physical measurement approach
  • Consistent Performance: Works in any geographic location

GPS Altitude Limitations:

  • Tidal Variations: Would require complex tide prediction systems
  • Geodetic Complexity: Multiple coordinate system transformations needed
  • Geographic Dependencies: Different datums and reference systems by region

Range Calculation Accuracy​

Accurate waterline calibration is critical for Lookout+ Nav range measurements:

  • Monocular Ranging: Uses water surface intersection calculations
  • Error Propagation: Waterline errors directly affect all range estimates
  • Close Object Accuracy: Most important for nearby object detection

Troubleshooting​

Common Issues​

Inconsistent Range Measurements:

  • Check waterline offset accuracy
  • Verify vessel loading hasn't changed significantly
  • Confirm INS position hasn't shifted

Objects Appearing Above/Below Expected Positions:

  • Waterline Z offset may have incorrect sign (should be negative)
  • Physical measurement may be inaccurate
  • Camera mounting may have changed

Cross-Camera Inconsistencies:

  • Individual camera offsets may need adjustment (contact Greenroom)
  • Transform tree relationships may be incorrect
  • System timing issues between sensors

Verification Methods​

Known Object Testing:

  • Use fixed markers or buoys at known distances
  • Compare Lookout+ measurements to manual estimates
  • Check consistency across different ranges

Cross-Reference with Charts:

  • Compare detected object positions with chart features
  • Verify coastline and navigation marker positions
  • Check against AIS/radar when available

Best Practices​

Documentation​

  • Record All Changes: Document waterline offsets and date of changes
  • Vessel Specifications: Note typical loading conditions used for calibration
  • Contact Information: Keep Greenroom engineer contact details readily available

Regular Verification​

  • Periodic Checks: Verify range accuracy during routine operations
  • Loading Changes: Recalibrate if vessel loading patterns change significantly
  • Seasonal Adjustments: Consider changes in equipment or ballast
Deployment Best Practices

For deployable systems, create a standardized measurement and configuration procedure. This ensures consistent, accurate setup across different vessels and reduces the chance of configuration errors.