DOC 07REFERENCE
Conventions, units and glossary
A one-page reference for the conventions used throughout LEVIATHAN and its exports, and for the terms used in this documentation.
Frames
| Frame | x | y | z | Origin |
|---|---|---|---|---|
| World (NED) | north | east | down | Sea surface |
| Body (FRD) | forward | starboard | down | Centre of gravity |
| Camera (OpenCV optical) | right | down | forward (optical axis) | Camera centre |
| Acoustic / inertial sensor (FRD) | boresight | starboard | down | Sensor origin |
Attitude is roll, pitch and yaw applied in ZYX order. A transform TA_B maps points from frame B into frame A, and transforms compose as TA_C = TA_BTB_C. Pixel centres sit at integer coordinates, the principal point is ((W−1)/2, (H−1)/2), and image row 0 is at the top.
Units
| Quantity | Unit |
|---|---|
| Length, depth, range | m (depth positive down) |
| Angle | rad internally; degrees where the interface says so |
| Velocity, angular rate | m/s, rad/s |
| Force, moment | N, N·m |
| Simulation time | integer ns (canonical World); s elsewhere |
| Pressure | Pa |
| Temperature, salinity | °C, PSU |
| Sound speed | m/s |
| Absorption | dB/km (reported), dB/m (applied) |
| Frequency | Hz (sonar hardware), kHz (absorption tables) |
| Beam attenuation | 1/m per colour channel |
| Camera radiance | sr⁻¹, relative to surface irradiance |
| Sonar return | dimensionless, relative to source intensity at 1 m on axis |
| Optical flow, motion field | px over the interval; px/s |
Maturity labels
| Label | Meaning |
|---|---|
| Canonical | Computed from an immutable World snapshot; content-addressed, with declared units, frames and validity |
| Analytic | A closed-form or low-order physical model evaluated by the simulation service |
| Reference-checked | Tested against LEVIATHAN's own CPU reference; not a real-world validation |
| Validated in simulation | Tested against simulated truth over seeded, held-out scenarios, including faults and noise. No real-world evidence. |
| Partial, Baseline | Works in part with a key limit open, or exists with minimal evaluation. Used for perception algorithms. |
| Legacy | Kept for compatibility; superseded by a canonical product |
| Under review | Implemented and available from the service, but still under internal review; its contract may change. |
| Interface | An adapter that works when the external software is present |
| Preset parameters | Simulation values with recorded provenance; not manufacturer specifications |
Glossary
- Analytic tier
- The part of the simulation service that runs scenario rollouts and analytic models in floating-point time.
- Canonical World
- A live, multi-vehicle simulation on an integer-nanosecond clock that produces immutable snapshots for ground truth.
- Capture group
- All sensor samples taken at the same committed tick, one snapshot per sensor.
- Contributor
- One sonar ray sample that landed in a range–azimuth cell and added to its return.
- Correspondence
- The location and visibility, at a second snapshot, of the surface point a pixel sees at the first.
- ESKF
- Error-state extended Kalman filter: the canonical localization estimator, which propagates with the IMU and is aided by DVL, pressure, magnetometer and USBL.
- FAB Engine
- LEVIATHAN's physics and sensing core: dynamics, ocean environment, underwater optics and acoustics.
- Hull atlas
- The Hull workspace's grid of cells over a hull's wetted surface, used to address fouling, cleaning and inspection.
- KRAKEN
- LEVIATHAN's evaluation layer: trajectory data (K1), stage-attributed verification (K2) and fidelity and transfer analysis (K3).
- Localization estimate
- The estimator's published state for one vehicle at one time: pose, velocity, biases, covariance, status, health and provenance, with no ground truth inside.
- Material point
- A point fixed on a surface, identified by element, triangle and barycentric coordinates, followed through motion.
- Motion field
- The instantaneous image velocity of each pixel's material point, in pixels per second.
- Observability
- Whether the sonar acoustically observes an object at a sample, and if not, why.
- PerceptionFrame
- LEVIATHAN's scientific camera frame: geometry, labels and radiometry from one geometry pass.
- Project
- A folder registered in the Code workspace, optionally with a run command that the Training runs panel can launch.
- Radiometric validity
- A per-pixel flag stating whether the whole light path is modelled; where it is not, radiometric values are null.
- Range
- Euclidean distance along a pixel ray or sonar ray. Never interchanged with z-depth.
- Relative return
- The canonical sonar's dimensionless modelled return relative to the source; not a calibrated level.
- Scene document
- The serialisable description of a canonical scene from which a World is built.
- Sensor packet
- A typed, timestamped, immutable view of one canonical measurement, including its validity; the input to the localization estimator.
- Snapshot
- An immutable, hashed copy of the World state at one tick, as seen by one sensor.
- Stage mix
- How a task's episodes ended: never engaged, engaged but not acquired, acquired then lost, or succeeded.
- Track
- One life of one scene entity across samples, the unit of object ground truth.
- Validity code
- A per-cell or per-pixel code saying whether a value is modelled and, if not, why.
- Z-depth
- Distance of a point along the camera's optical axis.