AISsegments

A Python toolkit for compressing AIS vessel trajectories into compact, query-friendly linestring segments — without losing the kinematic features that maritime safety and risk analysis depend on.

What is this?

aissegments takes raw AIS position reports (millions of pings per day in a busy sea area) and outputs a small number of constant-COG/SOG linestring segments per vessel, one row per (vessel, time-window, course/speed). The output is shaped to drop straight into a PostGIS LINESTRING table.

It is the reference Python implementation of the Top-Down Kinematic Compression (TDKC) algorithm of Guo, Bolbot & Valdez Banda (Ocean Engineering 312 (2024), 119189), with the recursion-termination and adaptive-threshold fixes described in the paper.

Goals

1. Shrink AIS data without losing the maritime-relevant features. A continent-scale AIS feed easily produces hundreds of millions of position reports per month. Most of those points are uninformative — a vessel cruising in a straight line at a steady speed needs only its endpoints. TDKC keeps the points where vessels actually do something interesting (turn, accelerate, stop, manoeuvre) and drops the rest.
2. Treat AIS as a sequence of kinematic states, not just positions. The classical Douglas-Peucker simplification looks only at how far points stray from a straight line. That throws away course and speed changes that lie on a straight track, which are exactly the events maritime risk analysis cares about. TDKC uses both position (Synchronous Euclidean Distance) and velocity (Synchronous Velocity Difference) with adaptive per-track thresholds.
3. Produce database-ready output. The output isn't a smaller list of points — it's a list of Segment records with start/end coordinates, mean COG/SOG, and the count of original observations spanned. Each segment is a 2-point LINESTRING ready for ST_Intersects and other PostGIS operations.
4. Stay framework-neutral. The core depends only on NumPy. AISdb is an optional adapter (pip install "aissegments[aisdb]"); other input paths (CSV from Marine Cadastre / institutional exports / your own pipeline) work via read_csv_tracks without any extra dependencies.

Who is this for?

• Maritime risk analysts who need to run collision/grounding/allision queries against millions of vessel positions per area-year and want the spatial+temporal index to fit in memory.
• AIS data engineers maintaining a Postgres/PostGIS warehouse of vessel tracks and looking for a principled way to densify ingestion without overwhelming storage.
• Researchers reproducing or extending Guo et al.'s adaptive trajectory compression work.

What it produces

• tdkc(track) — same Track interface but with only the key points retained (typically 1-5% of the input, depending on track shape and threshold tuning).
• tdkc_segments(track) — a list of Segment records, one per consecutive key-point pair, ready for direct insertion as PostGIS LINESTRING(start_lon start_lat, end_lon end_lat) geometries with cog_mean, sog_mean, and n_points (count of original AIS pings each segment represents).

Why not just use Douglas-Peucker?

DP and its variants throw away every point that lies on a straight line, regardless of whether the vessel's behaviour is changing. A vessel slowing from 15 to 5 knots while continuing to head east — DP keeps two points (start, end) and you lose the entire speed change. TDKC keeps the deceleration point because its velocity vector has shifted. See docs/algorithm.md for the precise math, and examples/output/03_min_svd_sweep.png for a visual side-by-side.

Companion package

OMRAT (Open Maritime Risk Analysis Tool) — a QGIS plugin for collision/grounding/allision risk modelling — uses AISsegments as its segment-ingestion backend. The OMRAT pipeline shows a complete end-to-end flow: NMEA / CSV → aisdb decode → TDKC compression → bulk-load into a year-partitioned PostGIS schema.

Install

pip install aissegments

# with the optional AISdb adapter for ingestion from raw NMEA / CSV
pip install "aissegments[aisdb]"

For development with full test + coverage tooling:

git clone https://github.com/axelHorteborn/AISsegments
cd AISsegments
pip install -e ".[dev,aisdb]"
pytest --cov

Quickstart

import numpy as np
from aissegments import Track, tdkc, tdkc_segments

# Build a Track from your own arrays (lat/lon in degrees, sog in knots, cog in degrees).
track = Track.from_arrays(
    mmsi=219000123,
    t=np.array([0, 60, 120, 180, 240], dtype=float),     # unix seconds
    lon=np.array([12.0, 12.001, 12.002, 12.003, 12.004]),
    lat=np.array([55.0, 55.0, 55.0, 55.0, 55.0]),
    sog=np.array([10.0, 10.0, 10.0, 10.0, 10.0]),
    cog=np.array([90.0, 90.0, 90.0, 90.0, 90.0]),
)

# Compress: returns a Track containing only the key points.
compressed = tdkc(track)
print(len(compressed), "key points kept out of", len(track))

# Or go straight to segment records (one per consecutive key-point pair).
segments = tdkc_segments(track)
for s in segments:
    print(s.t_start, s.t_end, s.cog_mean, s.sog_mean, s.n_points)

Using AISdb as an input adapter

aissegments can consume the per-vessel track dicts produced by AISdb's TrackGen():

import aisdb
from aissegments.adapters import from_aisdb_track
from aissegments import tdkc_segments

with aisdb.SQLiteDBConn(dbpath="ais.db") as conn:
    qry = aisdb.DBQuery(start=..., end=..., callback=aisdb.sql_query_strs.in_bbox_time)
    tracks = aisdb.TrackGen(qry.gen_qry(), decimate=False)
    for t_dict in tracks:
        track = from_aisdb_track(t_dict)
        for seg in tdkc_segments(track):
            ...  # write seg to your PostGIS table

What's in the package

Module	Purpose
aissegments.tdkc	TDKC algorithm: SED + SVD, Compression Binary Tree, adaptive thresholds, key-node identification
aissegments._types	Track and Segment dataclasses, to_segments helper
aissegments.adapters	Input adapters: from_aisdb_track, read_csv_tracks (Marine Cadastre etc.), read_csv_static_records for vessel-info extraction

Algorithm details

See docs/algorithm.md for the mathematical formulation, with equation references back to the source paper.

Citation

If you use this package in academic work, please cite both the software and the underlying paper:

Guo, S., Bolbot, V., & Valdez Banda, O. (2024). An adaptive trajectory compression and feature preservation method for maritime traffic analysis. Ocean Engineering, 312, 119189. https://doi.org/10.1016/j.oceaneng.2024.119189

A CITATION.cff is included so GitHub renders a "Cite this repository" widget.

License

MIT — see LICENSE.