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arxiv: 2604.13292 · v1 · submitted 2026-04-14 · 💻 cs.CV

See&Say: Vision Language Guided Safe Zone Detection for Autonomous Package Delivery Drones

Pith reviewed 2026-05-10 15:46 UTC · model grok-4.3

classification 💻 cs.CV
keywords drone deliverysafe zone detectionvision-language modeldepth fusionhazard detectionsafety mapsurban environmentsautonomous systems
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The pith

Vision-language guidance fuses depth and detection to create reliable safety maps for drone package drops.

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

The paper proposes See&Say, a framework that combines geometric cues from monocular depth with semantic information from open-vocabulary detection, all refined iteratively by a vision-language model. This setup addresses the difficulty of picking safe drop zones for autonomous drones in cluttered urban areas where primary landing spots may be blocked by people or objects. If the integration works as described, drones gain the ability to spot hazards dynamically and suggest backup zones during the final approach phase. A reader would care because current geometry-only or segmentation-only methods often fail to reason about context in changing environments with moving activity.

Core claim

See&Say fuses monocular depth gradients with open-vocabulary detection masks to produce safety maps, while the vision-language model dynamically adjusts object category prompts and refines hazard detection across time. When the primary drop area is occupied or unsafe, the system identifies alternative candidate zones. On a curated dataset of urban delivery scenarios with moving objects and human activity, the approach records the highest accuracy and IoU for safety map prediction and stronger results in alternative zone evaluation across thresholds compared with baselines.

What carries the argument

Fusion of monocular depth gradients with open-vocabulary detection masks, guided by a vision-language model for iterative prompt adjustment and hazard refinement.

If this is right

  • Drones can produce more accurate safety maps for package drop decisions in cluttered settings.
  • Alternative drop zones become available when the primary pad is occupied or unsafe.
  • Performance holds across multiple evaluation thresholds for zone selection.
  • The final delivery phase gains robustness under time-varying conditions.
  • Integrated semantic and geometric reasoning outperforms isolated geometry or segmentation approaches.

Where Pith is reading between the lines

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

  • The same fusion pattern could apply to ground robots needing to choose safe stopping spots in crowds.
  • Open-vocabulary detection reduces dependence on hand-curated lists of hazards.
  • Real-time versions might feed directly into onboard flight controllers for live replanning.
  • Dataset collection focused on moving urban elements could serve as a benchmark for related perception tasks.

Load-bearing premise

The vision-language model can reliably and dynamically adjust object category prompts and refine hazard detection across time in dynamic urban conditions with moving objects and human activities.

What would settle it

A sequence of real urban drone footage in which moving pedestrians or changing lighting cause the generated safety map to flag an actually safe zone as hazardous or miss a clear hazard, yielding accuracy and IoU no better than depth-only or segmentation-only baselines.

Figures

Figures reproduced from arXiv: 2604.13292 by Mahyar Ghazanfari, Peng Wei.

Figure 1
Figure 1. Figure 1: Overview of the proposed See&Say framework. The system takes batches of five RGB frames and corresponding monocular depth maps as input. Depth gradients provide geometric cues for flatness and obstacle detection, while DINO-X produces open-vocabulary semantic hazard masks. These initial maps are fused to form a preliminary safety overlay. A VLM refines detection prompts using temporal RGB–depth context, im… view at source ↗
Figure 2
Figure 2. Figure 2: The VLM refines the object categories used by DINO-X [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The second VLM agent in See&Say incorporates human preferences into package drop zone selection, operating after the initial safety map is generated by the first VLM agent. where w,h are the bounding-box sides; otherwise we use a default r. For each candidate c, let S_c be its disk support and B^{\text {final}}_t the final unsafe mask. We define the safe ratio \mathrm {safe}(c)=1-\frac {1}{|S_c|}\sum _{(x,… view at source ↗
Figure 4
Figure 4. Figure 4: Qualitative comparison of pipeline stages across three scenes. Columns: (a) RGB input, (b) monocular depth, (c) initial DINOx [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: ROC curves (top row) and Precision–Recall curves (bottom row) shown across thresholds from left to right. True positive rate [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Score distributions for human preference evaluation [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
read the original abstract

Autonomous drone delivery systems are rapidly advancing, but ensuring safe and reliable package drop-offs remains highly challenging in cluttered urban and suburban environments where accurately identifying suitable package drop zones is critical. Existing approaches typically rely on either geometry-based analysis or semantic segmentation alone, but these methods lack the integrated semantic reasoning required for robust decision-making. To address this gap, we propose See&Say, a novel framework that combines geometric safety cues with semantic perception, guided by a Vision-Language Model (VLM) for iterative refinement. The system fuses monocular depth gradients with open-vocabulary detection masks to produce safety maps, while the VLM dynamically adjusts object category prompts and refines hazard detection across time, enabling reliable reasoning under dynamic conditions during the final delivery phase. When the primary drop-pad is occupied or unsafe, the proposed See&Say also identifies alternative candidate zones for package delivery. We curated a dataset of urban delivery scenarios with moving objects and human activities to evaluate the approach. Experimental results show that See&Say outperforms all baselines, achieving the highest accuracy and IoU for safety map prediction as well as superior performance in alternative drop zone evaluation across multiple thresholds. These findings highlight the promise of VLM-guided segmentation-depth fusion for advancing safe and practical drone-based package delivery.

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

3 major / 1 minor

Summary. The manuscript proposes See&Say, a framework for identifying safe package drop zones for autonomous delivery drones in cluttered urban environments. It fuses monocular depth gradients with open-vocabulary segmentation masks and uses a Vision-Language Model (VLM) for iterative prompt adjustment and hazard refinement across time to handle dynamic conditions such as moving objects and human activity. When the primary zone is unsafe, the system identifies alternative candidate zones. The authors curate a custom dataset of urban scenarios and report that See&Say outperforms all baselines on accuracy and IoU for safety map prediction as well as on alternative-zone metrics across multiple thresholds.

Significance. If the empirical claims can be substantiated with rigorous validation, the work offers a practical integration of geometric cues, open-vocabulary detection, and VLM reasoning for safety-critical drone decisions. The emphasis on dynamic urban conditions and alternative-zone fallback addresses a concrete deployment gap in autonomous delivery systems.

major comments (3)
  1. [§4] §4 (Experimental Results): The abstract asserts that See&Say achieves the highest accuracy and IoU for safety map prediction plus superior alternative-zone performance, yet supplies no baseline definitions, dataset size, number of sequences, error bars, or statistical tests. This absence prevents assessment of the central outperformance claim.
  2. [§3 and §4] §3 (Method) and §4 (Experiments): No ablation is reported that isolates the VLM iterative refinement and dynamic prompt adjustment from the underlying depth-gradient + open-vocabulary mask fusion. Without this isolation, especially on sequences containing motion, it remains unclear whether the reported gains are attributable to the VLM component emphasized in the abstract.
  3. [§4] §4 (Experiments): The manuscript provides no quantitative analysis of VLM prompt stability, false-negative reduction, or failure cases on moving objects and human activities, which are the exact conditions cited as motivation for the VLM-guided approach.
minor comments (1)
  1. [Abstract] Abstract: Consider adding one sentence on the specific VLM backbone and the number of baselines compared to give readers immediate context for the claimed superiority.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive and detailed comments. We address each major point below and will incorporate the suggested improvements in the revised manuscript to strengthen the empirical validation.

read point-by-point responses
  1. Referee: [§4] §4 (Experimental Results): The abstract asserts that See&Say achieves the highest accuracy and IoU for safety map prediction plus superior alternative-zone performance, yet supplies no baseline definitions, dataset size, number of sequences, error bars, or statistical tests. This absence prevents assessment of the central outperformance claim.

    Authors: We agree that the current presentation lacks sufficient detail for rigorous evaluation. In the revised manuscript we will expand §4 to explicitly define all baselines, report the exact size of the curated urban dataset (including number of scenarios, sequences, and frames), provide error bars from multiple runs or cross-validation, and include statistical significance tests (e.g., paired t-tests or Wilcoxon tests) comparing See&Say against baselines. The abstract will be updated if necessary to reference these additions. revision: yes

  2. Referee: [§3 and §4] §3 (Method) and §4 (Experiments): No ablation is reported that isolates the VLM iterative refinement and dynamic prompt adjustment from the underlying depth-gradient + open-vocabulary mask fusion. Without this isolation, especially on sequences containing motion, it remains unclear whether the reported gains are attributable to the VLM component emphasized in the abstract.

    Authors: We acknowledge the value of isolating the VLM contribution. We will add a dedicated ablation study in the revised §4 that compares the full See&Say pipeline (with VLM iterative refinement and dynamic prompt adjustment) against the base depth-gradient + open-vocabulary mask fusion without the VLM. Results will be reported separately on static and motion-containing sequences to quantify the incremental benefit of the VLM component. revision: yes

  3. Referee: [§4] §4 (Experiments): The manuscript provides no quantitative analysis of VLM prompt stability, false-negative reduction, or failure cases on moving objects and human activities, which are the exact conditions cited as motivation for the VLM-guided approach.

    Authors: We agree that quantitative characterization of the VLM's role under dynamic conditions is needed. In the revision we will add metrics for prompt stability across frames, quantitative false-negative reduction on moving objects and humans, and a breakdown of failure cases with examples drawn from the dataset. These will be presented in §4 alongside the existing results. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The manuscript describes an applied vision-language system for drone drop-zone detection that fuses monocular depth with open-vocabulary masks and uses a VLM for prompt refinement. No equations, derivations, fitted parameters renamed as predictions, or self-citation chains appear in the provided text. All performance claims are empirical (accuracy, IoU, alternative-zone detection) evaluated on a curated dataset; none reduce by construction to the inputs or to prior self-authored results. The work is self-contained as a descriptive engineering contribution.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The approach rests on domain assumptions about VLM capabilities rather than new free parameters or invented entities; no quantitative fitting or ad-hoc constants are described.

axioms (1)
  • domain assumption Vision-language models can effectively reason about scene safety and dynamically adjust prompts for hazard detection in real time
    Invoked when describing VLM guidance for iterative refinement during the final delivery phase.

pith-pipeline@v0.9.0 · 5523 in / 1209 out tokens · 37767 ms · 2026-05-10T15:46:01.794703+00:00 · methodology

discussion (0)

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    Determine if the landing pad issafefor the current frame (true/false). Decide based on thefinalframe and the previous 5 frames: if there are objects on the landing pad, or there will be objects on the landing pad, declare unsafe, otherwise declare safe

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    Provide a singleupdated prompt list: include ALL un- safe objects/surfaces; remove safe ones (e.g.landing pad if confirmed safe, bushes, . . . ). The list must reflect the most recent scene. Unsafe objects include any moving or static objects that are not flat, or are moving and not safe for a package drop. If the drop zone with H sign is un- safe, also a...

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    ranked": [ {

    Determine whether the primary landing pad with an ‘H’ marking is safe for a drop. Setlanding_pad_safe = falseonlyif you can see any object(s)insidethe landing pad area. Otherwise, setlanding_pad_safe = true. If you cannot locate the landing pad, set it tonulland explain. 2.reasoning: 1–3 short sentences describing what you see onthe pad. 3.future_predicti...