Fast Iterative Search and Sampling: map-aware trajectory planning for autonomous driving.
FISS (RA-L 2022) · FISS+ (IROS 2023) and the FOP baselines in one C++17 core, with Python bindings, ROS 2 / ROS 1 nodes and an MPC controller.

_{CARLA 0.9.16: FISS+ drives through 49 vehicles of mixed traffic, changing lanes to pass slower cars. Amber: executed plan · teal: candidate trajectories · inset: planner view.}

▶ Try the interactive replay in your browser · Inspect runs in Foxglove · Documentation · Notebook

News — v1.0.0 (October 2026). FISS, FISS+ and the FOP baselines are now one project, here: a C++17 core with pip install fiss-planner, ROS 2 / ROS 1 nodes and CARLA / CommonRoad / Lanelet2 support. It continues the former frenet_planner (frenet_optimal_planner) and fiss_plus_planner repositories. Announcement · Release notes

Why FISS Planner

• Sub-millisecond planning. FISS and FISS+ find near-optimal trajectories while generating 5–11× fewer candidates than exhaustive search. A full planning cycle takes 0.2–1 ms.
• Four planners, one interface. Switch between fop, fop_plus, fiss and fiss_plus with one parameter, even while the vehicle is driving.
• Map-aware. Supports Lanelet2, CommonRoad and CARLA maps. The planner:
  • plans real lane changes using each neighbouring lane's own geometry;
  • only changes lanes where that's legal;
  • caps speed by the speed limit and road curvature;
  • counts the lane changes the route still needs and makes them in time for the goal, earlier when more are needed;
  • stops at red lights.
• Keeps its distance.
  • Follows slower traffic at a set time headway, and overtakes when a neighbouring lane is free.
  • Stops behind stopped vehicles and at red lights at a set gap, with Werling-style following and stopping candidates.
  • Costs for headway, time to collision and lateral clearance shape every candidate.
  • A hard "virtual bumper" (minimum gap and time to collision) rejects anything closer, with a reaction-time grace for cut-ins.
  • Keeps a time gap to crossing and oncoming traffic, so an unprotected turn waits for a gap instead of squeezing past.
• Safe by construction.
  • Every trajectory is checked against vehicle limits, road edges and time-stamped obstacle predictions.
  • Obstacles are predicted along their lanes of the map, including tracked objects that arrive with only their current state.
  • Plans stay consistent between cycles through trajectory stitching.
  • When nothing is safe: keep the previous plan, re-plan with the safety envelope as a cost (the plan that breaches it least wins), then over a shorter horizon, and only then brake.
• Explainable. Every cycle reports why candidates were rejected, which obstacle blocked the best one, and the gap, headway and time to collision to the vehicle ahead. Record any run for Foxglove and scrub through it frame by frame.
• From planning to control.
  • An optional QP smoother refines the chosen trajectory inside a space–time driving corridor.
  • An LTV-MPC tracks it with 1–2 cm lateral error in CARLA.
• Runs everywhere. pip install fiss-planner, ROS 2 components, a ROS 1 node, or plain CMake.

Gallery

Same merge, three planners. FOP evaluates every candidate (about 170 per cycle here); FISS explores about 17 and FISS+ about 60 to reach the same result.
Dense traffic, US-101 (NGSIM recording)	Unprotected left turn at a T-junction: FISS+ lets the oncoming car pass first
Zipper merge	Urban arterial, Lankershim Blvd (NGSIM)
CARLA: overtaking a parked car	CARLA: a car cuts in; FISS+ brakes and moves over a lane

Quick start

pip install fiss-planner

import numpy as np
import fiss_planner as fp

x = np.arange(0.0, 300.0, 5.0)
road = fp.ReferenceLine(x, np.zeros_like(x))                     # any polyline
lanes = fp.Corridor.parallel_lanes(0.0, road.length, 3.5, 1, 0)  # ego lane + one lane to the left
parked = fp.predict_constant_velocity(1, 45.0, 0.0, 0.0, 0.0, 4.5, 1.9, horizon=6.0, dt=0.1)

planner = fp.make_planner(fp.make_config("fiss_plus"))
result = planner.plan(fp.FrenetState(s=10.0, s_d=10.0), road, lanes, [parked], target_speed=12.0)
print(result.success, result.trajectory.lane)  # True 1  -> overtakes in the left lane, in < 1 ms

fp.LocalPlanner wraps the whole pipeline (map, stitching, speed policy, smoothing, fail-safes): call step(t, ego, obstacles) every cycle. See the notebook and the Python guide.

ROS 2

ros2 launch fiss_planner_ros2 planner.launch.py odom:=/localization/odom \
    obstacles:=/perception/obstacles lanelet2_map:=/maps/town.osm controller:=true
ros2 param set /fiss_planner planner.type fiss      # switch planners live

The planner node publishes ~/trajectory (time-parameterized x, y, yaw, v, a, κ), ~/path, ~/candidates, ~/markers (scene; rviz:=true opens RViz 2) and ~/stats. The controller node publishes ackermann_msgs/AckermannDriveStamped. ROS 1 Noetic has the same interface (roslaunch fiss_planner_ros1 planner.launch). See docs/ros.md.

Planners

	How it searches	Paper
fop	generates every candidate, keeps the cheapest valid one	Werling et al., ICRA 2010
fop_plus	generates every candidate, validates lazily in cost order
fiss	iterative search over the end-state grid, guided by the previous solution	Sun et al., RA-L 2022
fiss_plus	best-first exploration plus continuous end-state refinement	Sun et al., IROS 2023

All four share sampling, costs and validation, so they are directly comparable and interchangeable. The code as published with the papers is kept at tag paper-ral2022 (FISS) of this repository and at fiss_plus_planner@paper-iros2023 (FISS+).

Results

CommonRoad, closed loop. 280 public scenarios: all 130 NGSIM recordings plus 150 hand-crafted ones. Success uses the official CommonRoad goal check (place, time window, speed and heading) with no collision and no road-boundary violation. The QP smoother is on.

Planner	Success	Collision	Plan time (mean)	Trajectories per cycle
fop	76.1 %	2.1 %	9.1 ms	210
fop_plus	76.1 %	2.1 %	1.2 ms	210 generated · 14 validated
fiss	75.7 %	1.8 %	0.7 ms	19
fiss_plus	74.6 %	2.1 %	0.9 ms	44

Keeping distance cuts the time spent below 1 s of headway to under a third and more than halves the runs that come within 0.5 m of another road user, at the same collision rate. In the replayed logs it costs success, because recorded traffic does not open the gaps it asks for. With predictions from the current state only, map-aware lane-following prediction succeeds in 70.7 % against 69.3 % for constant velocity, with fewer collisions.

CARLA 0.9.16, closed loop.

• Runs: 40 runs, all collision-free: lead vehicle, parked car, scripted cut-in and dense traffic, with every planner and both controllers. In the scripted cut-in, the tightest, the car stays 0.5–0.8 m away.
• Dense traffic, ten seeds: no collisions, no emergency braking, no time below 1 s of headway, and no stops for passing traffic. 99.5 % of cycles are planned; in queues the ego stops a few metres behind the car ahead.
• Planning time: 0.1–0.7 ms (FISS/FISS+).
• Tracking: MPC lateral error 1–2 cm RMS.

ROS 2 bag replay. 20 NGSIM recordings were replayed through the ROS 2 node. Plans stay within 1.3–1.4 m of the human driver's path over 3 s on average, at 2.4–3.2 ms per node cycle (FOP+, FISS, FISS+).

Full tables, protocols and ablations are in docs/benchmarks.md; raw results are in benchmarks/results/.

Integrations

Python	pip install fiss-planner (Linux, macOS; Python 3.10–3.13)
ROS 2	fiss_planner_ros2: Jazzy, Humble; component nodes, live parameters
ROS 1	fiss_planner_ros1: Noetic; dynamic_reconfigure
Maps	Lanelet2 (C++ adapter with routing), CommonRoad, CARLA
Simulation	CommonRoad closed-loop benchmark, CARLA closed loop and video recorder, ROS 2 bag tools
C++	find_package(fiss_planner); only yaml-cpp, plus OSQP for the optional smoother/MPC

Build from source / run the tests

git clone https://github.com/SS47816/fiss_planner.git && cd fiss_planner
# with pixi (no root needed; ROS from RoboStack)
pixi run test                    # C++ core (GoogleTest)
pixi run -e bench py-test        # Python bindings
pixi run -e jazzy ros2-test      # ROS 2 packages
pixi run -e noetic ros1-test     # ROS 1 packages
# or into a ROS 2 workspace
colcon build --base-paths fiss_planner/{core,msgs,ros/ros2}

Reproduce the benchmarks and demos

python benchmarks/commonroad/fetch_scenarios.py --out data/cache/scenarios --bench-set data/cache/bench_set
pixi run -e bench python -m fiss_planner.commonroad.benchmark --scenarios data/cache/bench_set --smoother
pixi run -e bench python -m fiss_planner.commonroad.demo data/cache/bench_set/ZAM_Zip-1_50_T-1.xml \
    --panels fop fiss fiss_plus --gif compare.gif
# CARLA (start $CARLA_ROOT/CarlaUE4.sh -RenderOffScreen first)
pixi run -e carla python -m fiss_planner.carla.closed_loop --planner fop fiss fiss_plus
pixi run -e carla python -m fiss_planner.carla.record --scenario cut_in --mp4 cut_in.mp4

How it works

flowchart LR
  M[Lanelet2 / CommonRoad / CARLA map] --> R[Route corridor: reference line + lane bands]
  O[Obstacles + predictions] --> P
  E[Ego state] --> S[Stitching] --> P
  R --> P["Planner: FOP | FOP+ | FISS | FISS+"]
  P --> Q[QP smoother - optional]
  Q --> T[Trajectory] --> C[MPC / Stanley]

Loading

End states are sampled over lateral offset (per lane) × target speed × horizon. Lateral motion is a quintic polynomial and longitudinal motion a quartic; both are converted to Cartesian space analytically. The planners differ only in how they search this grid. See docs/concepts.md.

Citation

If this project helps your research, please cite:

@article{sun2022fiss,
  author  = {Sun, Shuo and Liu, Zhiyang and Yin, Huan and Ang, Marcelo H.},
  title   = {{FISS}: A Trajectory Planning Framework Using Fast Iterative Search and Sampling Strategy for Autonomous Driving},
  journal = {IEEE Robotics and Automation Letters},
  volume  = {7}, number = {4}, pages = {9985--9992}, year = {2022},
  doi     = {10.1109/LRA.2022.3191940}
}
@inproceedings{sun2023fissplus,
  author    = {Sun, Shuo and Chen, Jie and Sun, Jiawei and Yuan, Chengran and Li, Yuanchen and Zhang, Tangyike and Ang, Marcelo H.},
  title     = {{FISS+}: Efficient and Focused Trajectory Generation and Refinement Using Fast Iterative Search and Sampling Strategy},
  booktitle = {IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
  pages     = {10527--10534}, year = {2023},
  doi       = {10.1109/IROS55552.2023.10341498}
}

Contributing

Issues, discussions and pull requests are welcome; see CONTRIBUTING.md.

Licensed under Apache-2.0.