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arxiv: 2605.17533 · v1 · pith:KF6FQILUnew · submitted 2026-05-17 · 📡 eess.SY · cs.RO· cs.SY

Distributed 3D Leader-Follower Formation Control with Field-of-View Safety via Control Barrier Functions

Pith reviewed 2026-05-19 22:26 UTC · model grok-4.3

classification 📡 eess.SY cs.ROcs.SY
keywords leader-follower formationcontrol barrier functionsfield of view safetymulti-UAV systemsdistributed controlperception-aware control3D formation trackingsafety filters
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The pith

Control barrier functions enforce field-of-view safety in 3D leader-follower UAV formations.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes a distributed control method for multiple UAVs to maintain 3D formations while ensuring each follower can always see the leader with its onboard camera. It starts with a relative kinematic model using line-of-sight coordinates to design a formation tracking controller that uses only local information. The key step is wrapping this controller inside a quadratic program based on control barrier functions that changes the velocities as little as possible to keep the leader in view. A sympathetic reader would care because losing sight of the leader breaks vision-based coordination, and this method builds in the guarantee by design rather than reacting after the fact.

Core claim

The central claim is that embedding a nominal 3D leader-follower formation tracking controller into a Control Barrier Function-based Quadratic Program safety filter minimally modifies the commanded velocities to maintain the leader inside the follower's camera frustum while preserving formation tracking whenever feasible. This architecture is derived from a relative kinematic model in line-of-sight coordinates and validated through Gazebo simulations and Crazyflie hardware experiments showing accurate tracking and effective FOV enforcement even when nominal commands conflict with visibility.

What carries the argument

The Control Barrier Function-based Quadratic Program (CBF-QP) safety filter, which takes the nominal formation velocity commands and finds the closest safe velocities that satisfy the field-of-view constraint.

If this is right

  • The leader stays visible to the follower at all times under the safety filter.
  • Formation tracking performance is preserved as long as the visibility constraint allows.
  • The method works in distributed fashion using only relative states.
  • Hardware experiments on Crazyflie drones confirm the approach in real conditions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This method could be combined with other safety constraints like collision avoidance for more complex swarm behaviors.
  • Extensions to non-holonomic vehicles or different sensor models might require adjusted barrier functions.
  • Guaranteeing feasibility of the QP under all operating conditions would allow fully reliable deployment without fallback strategies.

Load-bearing premise

The control barrier function quadratic program always admits a feasible solution at each time step under the conditions of the formation task.

What would settle it

A scenario or simulation where the desired formation geometry and velocities make it impossible for any velocity adjustment to keep the leader in the camera frustum, leading to either visibility loss or controller failure.

Figures

Figures reproduced from arXiv: 2605.17533 by Bin Hu, Immanuel R. Santjoko, Miao Pan, Richie R. Suganda.

Figure 1
Figure 1. Figure 1: Perception-aware leader–follower safe control. Without perception [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Leader–follower geometry and camera frustum. The leader position [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Perception-aware safe 3D-LFF control architecture. A high-level distributed 3D-LFF controller tracks the desired state [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Multi-UAV leader–follower navigation in a Gazebo cave environment. [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Gazebo simulation of the three-stage task. A comparison of 3D [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Gazebo simulation of abrupt leader motion. A comparison of 3D [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Trajectories of the leader and the followers during the three-stage [PITH_FULL_IMAGE:figures/full_fig_p006_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Hardware experiment of the three-stage task. A comparison of 3D [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗
read the original abstract

This letter proposes a distributed 3D leader-follower formation (3D-LFF) control framework for multi-UAV systems that achieves formation tracking while enforcing perception safety constraints. Maintaining safe, vision-based 3D-LFF is challenging because onboard cameras impose strict Field-of-View (FOV) limitations, and demanding formation commands can drive the leader outside the follower's camera frustum, resulting in loss of visibility. To address this issue, we develop a perception-aware safe control architecture that guarantees visibility by construction. First, we derive a relative kinematic model in a line-of-sight coordinate representation and design a distributed 3D-LFF tracking controller using only locally available relative states. Next, we embed the nominal formation controller within a Control Barrier Function-based Quadratic Program (CBF-QP) safety filter that minimally modifies the commanded velocities to maintain the leader inside the follower's camera frustum while preserving formation tracking whenever feasible. Gazebo simulations and Crazyflie hardware experiments validate the proposed approach, demonstrating accurate formation tracking and effective FOV enforcement, including scenarios in which the nominal desired formation conflicts with visibility constraints.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript proposes a distributed 3D leader-follower formation (3D-LFF) control framework for multi-UAV systems. It derives a relative kinematic model in line-of-sight coordinates, designs a nominal distributed formation tracking controller using local relative states, and embeds this controller in a CBF-QP safety filter that minimally modifies commanded velocities to enforce a field-of-view (FOV) constraint keeping the leader inside the follower's camera frustum. The approach is claimed to guarantee visibility by construction while preserving formation tracking whenever feasible, and is validated via Gazebo simulations and Crazyflie hardware experiments including conflict scenarios.

Significance. If the QP feasibility analysis and experimental verification are strengthened, the work offers a practical perception-aware safety filter for vision-based UAV formations that combines standard CBF theory with distributed formation control. This addresses a relevant engineering gap where demanding formation commands can violate onboard camera constraints.

major comments (1)
  1. [Abstract and §4] Abstract and §4 (Safety Filter Design): the central guarantee of visibility 'by construction' is qualified by 'whenever feasible,' yet the manuscript supplies neither a proof that the feasible set of the CBF-QP is non-empty for the closed-loop relative dynamics under the tested formation commands nor empirical verification (solver status flags, minimum constraint margins, or infeasibility counts) from the Gazebo and Crazyflie experiments.
minor comments (2)
  1. [Experiments] Experiments section: validation is described only qualitatively; quantitative metrics (e.g., RMS formation tracking error, percentage of time the FOV constraint is active, or histograms of QP slack variables) with error bars or statistical summaries across trials are absent.
  2. [§3] Notation and §3 (Relative Kinematics): the precise definition of the FOV barrier function h(x) derived from the line-of-sight angles and the choice of class-K function in the CBF inequality should be stated explicitly with the corresponding equation numbers.

Simulated Author's Rebuttal

1 responses · 1 unresolved

We thank the referee for the constructive feedback. We address the major comment below.

read point-by-point responses
  1. Referee: [Abstract and §4] Abstract and §4 (Safety Filter Design): the central guarantee of visibility 'by construction' is qualified by 'whenever feasible,' yet the manuscript supplies neither a proof that the feasible set of the CBF-QP is non-empty for the closed-loop relative dynamics under the tested formation commands nor empirical verification (solver status flags, minimum constraint margins, or infeasibility counts) from the Gazebo and Crazyflie experiments.

    Authors: We agree that the manuscript does not contain a formal proof that the CBF-QP feasible set remains non-empty under the closed-loop relative dynamics for the tested formation commands; deriving such a guarantee for the nonlinear distributed system is non-trivial. We will revise the manuscript to add empirical verification using data from the Gazebo simulations and Crazyflie experiments. This will include QP solver feasibility status, time histories of the minimum CBF value h(x), and confirmation of zero infeasibility events in the reported trials. The abstract and Section 4 will be updated to clarify that the visibility guarantee holds subject to QP feasibility, which is supported empirically for the presented scenarios. revision: partial

standing simulated objections not resolved
  • Formal proof that the CBF-QP feasible set is non-empty for the closed-loop relative dynamics under the tested formation commands

Circularity Check

0 steps flagged

No circularity; derivation uses standard CBF-QP on relative kinematics

full rationale

The paper derives a relative kinematic model in line-of-sight coordinates, designs a distributed nominal 3D-LFF tracking controller from locally available states, and then embeds that controller inside a standard CBF-QP safety filter whose barrier function enforces the FOV constraint. None of these steps reduce the claimed visibility guarantee to a fitted parameter, a self-referential definition, or a load-bearing self-citation whose validity depends on the present work. The 'whenever feasible' qualifier is an explicit acknowledgment of QP feasibility rather than a hidden circular assumption. The overall architecture therefore remains self-contained against external CBF theory and does not exhibit any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard assumptions from nonlinear control and optimization; no new physical entities are introduced. The main free parameters are the CBF class-K functions and QP weights that trade off formation error versus safety margin.

free parameters (2)
  • CBF gain and class-K function parameters
    These define the strictness of the FOV barrier and are chosen to make the QP feasible; their specific values are not given in the abstract.
  • QP weighting matrices
    Trade-off between nominal formation velocity and safety correction; must be tuned for each formation geometry.
axioms (2)
  • domain assumption The relative kinematic model in line-of-sight coordinates is accurate and the only states needed for control are locally measurable.
    Invoked when the distributed controller is designed using only relative states.
  • ad hoc to paper The quadratic program is feasible whenever the nominal formation command would violate the FOV constraint.
    The abstract qualifies the guarantee with 'whenever feasible' but does not prove non-emptiness of the feasible set.

pith-pipeline@v0.9.0 · 5744 in / 1651 out tokens · 42260 ms · 2026-05-19T22:26:53.659753+00:00 · methodology

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Reference graph

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