DOC 03SIMULATION CONTENT

Vehicles

LEVIATHAN has nine built-in vehicles: three remotely operated vehicles, four autonomous underwater vehicles, an autonomous surface vessel and a buoyancy-driven glider. You choose them from Vehicle in the Viewport, and you can import your own.

Catalogue

Each vehicle is shown side-on at the Shipwreck at the same camera distance. Viewport models are simplified representations for visualisation. The USV is not pictured: it rides the surface, above the Viewport's default underwater camera.

"BlueROV2 Heavy (faithful)" appears in the Dashboard's vehicle lists rather than in the Viewport menu. The glider is driven by its buoyancy engine and wings through a sawtooth dive-and-climb profile (Simulate → Glide). It is not part of the learning task suite, which uses thruster-driven vehicles.

Hydrodynamic coefficients

REMUS-100, HUGIN Survey and the torpedo AUV also use cross-flow drag along their slender hulls (coefficient 1.1). For these presets the strip integral supplies the sway, heave, pitch and yaw drag. The USV has a waterplane area of 1.1 m², transverse and longitudinal metacentric heights of 0.45 m and 1.8 m, and frontal and lateral wind areas of 0.42 m² and 0.95 m². Each fin-steered vehicle has a rudder and an elevator: 0.0095 m² each on the torpedo AUV, 0.014 m² on REMUS-100 and 0.18 m² on HUGIN.

Provenance

Before a run, a vehicle can be checked for physical coherence. Negative added mass, non-positive inertia or negative damping make the check fail. A hull that would sink or capsize produces a warning instead, because heavy landers and unstable hulls are legitimate test cases.

Body frame and sensor mounts

Every vehicle's body frame is FRD: x forward, y starboard, z down, with its origin at the centre of gravity (see Coordinate frames). In the canonical vehicle catalogue, each vehicle is a document of links and sensors. Every sensor declares a type, the link it is attached to, a mount transform and the frame convention of its type: OpenCV optical for cameras, sensor FRD for acoustic and inertial sensors. Mounts also record their source. The built-in camera mounts sit at the front of each hull, with the optical axis along body x; they are not measured from manufacturer CAD.

Reference vehicles

Besides the nine built-in vehicles, the canonical catalogue holds reference vehicles that are explicitly labelled as test and reference models, not production vehicles. They borrow the BlueROV2 Heavy physics preset and declare richer sensor sets, with declared test rates rather than device specifications. Two of them carry the navigation sensors the localization estimator uses.

Representing your platform

LEVIATHAN describes every vehicle the same way: a rigid body with mass, inertia, added mass and damping, plus thrusters, fins or wings, and sensors on declared mounts. The built-in presets cover the common classes. Your own robot fits the same model.

Canonical sensors are declared in a vehicle's catalogue model, with their mount transforms and sampling schedules: camera, sonar, DVL, IMU, pressure sensor, magnetometer and USBL. The canonical catalogue ships with LEVIATHAN and consists of the built-in and reference vehicles; imported and uploaded vehicles get physics, and the analytic sensors in the Viewport, but no canonical catalogue entry.

Custom vehicles

Import URDF, SDFormat or MJCF

Choose Vehicle → Import URDF / SDF / MJCF… and select a robot description. LEVIATHAN reads link geometry and inertial mass, fits a bounding hull, and estimates the hydrodynamic coefficients from it. Translational added mass comes from potential flow about the equivalent ellipsoid (Lamb), quadratic drag from the projected areas, and rotational terms and linear damping from heuristics you can tune. The vehicle is neutrally buoyant unless you give a density or mass. It is then registered and checked, and it appears in the vehicle lists.

Upload a CAD hull

Vehicle → Upload CAD… accepts glTF/GLB, OBJ, STL and COLLADA meshes. The mesh becomes a registered vehicle with physics derived from its geometry: volume, centre of buoyancy and projected areas are computed from the mesh. Each result comes with uncertainty bounds, which can seed domain randomisation. Registered hulls are kept in a local vehicle store as derived parameters with a content hash of the source geometry. They survive restarts and can be selected wherever a preset can, including the learning tasks. You can add thruster positions and directions, a mass or density, and a per-thruster force limit.

The FAB Engine also has a mesh-based hydrodynamics tier that integrates hydrostatic and hydrodynamic forces face by face over a closed mesh. It handles partial submergence and spatially varying flow, at roughly a hundred times the cost of the coefficient model per step. It is used where a body's geometry matters more than throughput, for example when binding bodies from Stonefish scenario files.