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Planets

Draft

This page is scaffolded. The outline below marks what it should cover.

A Planet (and the Earth preset) is a world-level entity that ties a planet-fixed frame to the shared fields.

To cover

  • The planet-fixed frame — axis + rotation rate, and the symbolic + numpy transforms between PlanetFrame and WorldFrame.
  • Cartesian surface geometry — base Planet is only a rotating Cartesian frame and uses radial scene-up. Earth separately owns the oblate WGS-84 ellipsoid used by its physical fields and collision surface. Datum and latitude/longitude conversion belong to the consuming device adapter; Manta accepts the resulting planet-fixed Cartesian point. A spherical Earth is Earth(flattening=0.0).
  • Standing disturbances — what Earth auto-registers on the world's shared fields: point-mass + J2 gravity (J2 on by default for the oblate Earth — with the spinning frame's centrifugal term it makes the ellipsoid an equipotential, so gravity is normal to the sea surface), an Ocean + ISA Atmosphere pair of fluid regimes (baseline media built on PlanetFrameFluid) split at the ellipsoid, the sea surface as a solid Ellipsoid collision obstacle, a dipole magnetic field.
  • Initial-state factories — earth.position(...), earth.velocity(...), earth.velocity(0, 0, 0) and how they resolve to WorldFrame seeds at compile time.
  • Scene — earth.scene_at(planet_point) returns a local East/North/Up frame fixed in the planet's body frame, used as numeric I/O glue while the dynamics stay in WorldFrame: scene.at_rest(...) for full rigid-attachment placement (orbital velocity + body spin rate + local-tangent attitude) in small scene-local coordinates, scene.relative(state) to report a craft's pose/velocity scene-relative, and scene.world_pose(t) to anchor rendering (publish the scene's world pose, log children relative to it, track it) so the planet can stay at its true scale at the world origin.
  • Multiple planets in one world, superposing into the shared fields.
  • Earth's rotation and the gyrocompass — sensing Earth-rate (see the gyrocompass demo).

Source material

  • Reference: Planets
  • Code: manta/planets/*.py