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limitations.md

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Limitations

ballistic-solver is a point-mass intercept solver for games, simulation, robotics, and research. It is deliberately scoped, and the assumptions below are part of that scope rather than bugs. Knowing them up front is the best way to decide whether it fits your use case.

Physical model

  • Point mass only. The projectile is a point with no orientation, no rigid- body dynamics, and no lift. There is no spin drift / Magnus effect.
  • Quadratic drag with a single scalar coefficient kDrag. There is no Mach-dependent drag table and no per-segment drag curve; transonic/supersonic rounds whose Cd varies strongly with speed are not modelled accurately.
  • Constant gravity. No altitude variation, no Coriolis term.
  • Uniform, constant wind. Wind is a single air-velocity vector; there is no gust, shear, or altitude profile.
  • Air density is folded into kDrag and is constant for the flight; it does not vary with altitude during the trajectory.

Solve scope

  • Two unknowns: launch angles (θ, φ) only. Muzzle speed v0 is an input, not solved for; the solver does not pick a charge/speed to make a target reachable.
  • Target motion is constant-velocity or constant-acceleration (or whatever a user-supplied predictor returns via solve_predicted). A freely maneuvering target is only handled to the extent the predictor models it.
  • One arc branch at a time. With arcMode fixed, the solver finds a solution on that branch; a solution that exists only on the other branch is not returned unless you switch arcMode.
  • No terrain or obstacle collision. Trajectories are not clipped against ground or geometry; an angle that "hits" may pass through terrain in your world.

Numerical behaviour

  • Fixed-step RK4. Accuracy depends on dt, tMax, and tolMiss. Too large a dt or too short a tMax can miss or fail to converge.
  • Best-effort, not guaranteed. For unreachable or near-limit targets the solver returns its closest iterate with success = false; it does not prove that no solution exists.
  • Your runtime must match the solver's physics. If the consuming engine integrates with a different scheme or timestep, the computed angles may not hit even when the solver reports success. See the "Solver validity note" in the README.

Not a fire-control system

This is a numerical library for simulated and robotic targeting and for research. It is not a certified or safety-rated fire-control system and is not intended for use as one.