Open-source purpose-built robots
Holding a survey line in current and waves: line-of-sight against integral line-of-sight for a small boat
research/marine-path
Plain line-of-sight guidance leaves a steady cross-track offset of delta*tan(asin(c/U)) in a cross current c (simulation matches it to 1%: 3.77 m at 0.3 m/s, 12 m look-ahead); integral LOS removes it, with lower rms cross-track error in 136 of 144 cross-current cases and the 8 exceptions all at a 6 m look-ahead with integral gain 2, where it oscillates (rms about 2.3 m even in still water)
7 tests
What it found
Milestone 1 of track 23's marine-path step, filed under the marine-hull programme. A stdlib 3-DOF (surge, sway, yaw) 200 kg boat with a rudder and surge PI, in a constant earth-frame current and a six-sinusoid wave disturbance (4 to 9 s periods, force scale swept, not sourced), follows a straight line under plain LOS and integral LOS (Borhaug, Pavlov and Pettersen 2008). Check: the simulated plain-LOS offset equals the analytic delta*tan(asin(c/U)) to 1% (0.3 m/s, 3.774 m). Sweep: cross current 0 to 0.5 m/s, wave scale 0 to 1, look-ahead 6, 12, 24 m, integral gain 0.5, 1, 2, 3 seeds. Integral LOS has lower rms cross-track error in 136 of 144 cases with current at least 0.2 m/s; the 8 exceptions are all look-ahead 6 m with gain 2, which oscillates. Energy per ground km differs by a median 1.4% (max 37%, in the oscillating cases, which also include the transient). Damping, rudder and wave-force coefficients are not sourced; the model has no Coriolis cross-coupling beyond u*r and v*r, no MPC arm, no JONSWAP spectrum and no field data. Preliminary; simulation only.
Research log
Ongoing: each run adds a batch and an entry, newest first. Source: LOG.md.
2026-10-30 · Milestone 1: LOS against integral LOS (hypotheses written before the sweep)
- H1: simulated plain-LOS offset equals delta*tan(asin(c/U)) within 1%. H2: ILOS has lower rms cross-track error than LOS in at least 90% of cases with current >= 0.2 m/s. H3: guidance changes energy per ground km by under 3% in the median.
- Outcome: H1 held (3.774 m, tested). H2 held, 136 of 144 (94%); the 8 misses are all delta = 6 m, kappa = 2 (integral oscillation, a finding I did not predict). H3: median 1.4%, but max 37% in the oscillating cases (median held, tail not).
- Limits: unsourced coefficients, sinusoid waves, start-up transient in the scores.
Paper, code and results
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.