gps-denied-onboard/_docs/00_research/00_ac_assessment.md

# Acceptance Criteria Assessment

Accessed: 2026-05-01. Rerun after user-approved clarifications: 2026-05-01.

## Research Scope

- **Output class**: Technical-component selection support.
- **Novelty sensitivity**: High for VPR, embedded AI, and autopilot integration; source preference is current papers and official docs.
- **Boundary**: Fixed-wing UAV, nadir navigation camera, ArduPilot Plane, Jetson Orin Nano Super, offline Azaion Suite Satellite Service cache, eastern/southern Ukraine terrain.

## Acceptance Criteria

| Criterion | Current Values | Researched Values / Evidence | Cost / Timeline Impact | Status |
|-----------|----------------|------------------------------|------------------------|--------|
| AC-1.1 / AC-1.2 frame-center accuracy | <=50 m for >=80%, <=20 m for >=50% in normal segments | Plausible only with periodic satellite anchoring plus VO/IMU propagation. Aerial VPR papers show the mechanism is viable but sensitive to weather, scale, repetition, and tile overlap. | High validation cost. | Keep, high-risk |
| AC-1.3 drift | VO-only <100 m, IMU-fused <50 m between anchors, anchor age reported | Updated AC now requires `last_satellite_anchor_age_ms`, binned validation, and degraded covariance after a solution-defined max anchor age. | Medium. | Updated |
| AC-1.4 confidence | 95% covariance ellipse + source label | `GPS_INPUT` supports accuracy fields; source labels must be carried in telemetry/FDR because `GPS_INPUT` has no semantic label field. | Medium. | Keep |
| AC-2.1 registration | VO >95%; satellite anchoring measured separately | Split is correct: VO success is not the same as cross-domain satellite anchor success. | Medium-high. | Updated |
| AC-2.2 reprojection | <1 px VO, <2.5 px satellite anchor | Reasonable image-space gates, with coordinate error still dependent on calibration, orthorectification, and satellite georegistration. | Medium. | Keep |
| AC-3.x resilience | Outliers, sharp turns, disconnected segments, blackout | Technically feasible only through mode switching: VO failure triggers VPR/relocalization, blackout triggers IMU-only propagation with honest covariance growth. | High test cost. | Keep |
| AC-4.1 latency | <400 ms p95, <=10% frame drops, heavy VPR conditional | Aerial VPR survey reports some re-ranking paths too slow for steady-state use; solution must keep global VPR off the per-frame hot path. | High optimization cost. | Updated |
| AC-4.2 memory | <8 GB shared | Feasible if descriptors are compressed/pruned and indices are memory-mapped or loaded selectively. | Medium-high. | Keep |
| AC-4.3 MAVLink | v1 GPS_INPUT only via pymavlink | ArduPilot docs require `GPS1_TYPE=14`; MAVLink defines required lat/lon, velocity, fix, and accuracy fields. MAVSDK should remain telemetry-oriented. | Medium. | Keep |
| AC-5.2 failsafe | >3 s no estimate triggers fallback, Plane SITL verified | Copter docs are reference only. Plane-specific production parameters must be verified in SITL. | Medium. | Updated |
| AC-7 object localization | Level-flight AI-camera object GPS | Realistic under level-flight clause; maneuvering estimates must publish conservative bound. | Medium. | Keep |
| AC-8.x satellite cache | 0.3-0.5 m/px, freshness, offline descriptors, VPR chunks | Resolution is feasible through commercial/service imagery. Storage must count descriptors unless separately budgeted. | Medium-high. | Updated |
| AC-NEW-1 / 2 startup and spoofing | <30 s first fix, <3 s promotion | Feasible only with prebuilt engines, warmed indices, and verified Plane GPS-health triggers. | Medium-high. | Keep with SITL gate |
| AC-NEW-3 FDR | <=64 GB per flight, no raw frames | Feasible with segment files and rollover. | Medium. | Keep |
| AC-NEW-4 / 7 safety budgets | False-position and cache-poisoning probabilities | Appropriate safety gates, but require Monte Carlo and representative flight/replay data. | High. | Keep |
| AC-NEW-5 environment | -20 C to +50 C, 25 W for 8 h | NVIDIA confirms 25 W mode; thermal design must prevent throttling. | Medium-high. | Keep |

## Restrictions Assessment

| Restriction | Current Values | Researched Values / Evidence | Cost / Timeline Impact | Status |
|-------------|----------------|------------------------------|------------------------|--------|
| Camera source of truth | `restrictions.md` pins ADTi 20MP ~5472 x 3648 | User confirmed `restrictions.md` is authoritative. Lens/FOV remains a design parameter. | Medium during module selection. | Updated |
| Fixed nadir camera | No gimbal stabilization | Good for orthorectification; turn/tilt requires attitude compensation and failure detection. | Medium. | Keep |
| Terrain/weather | Flat steppe/agricultural, seasonal classes included | Repetitive fields and seasonal changes are VPR hazards; validation must include those classes. | High validation cost. | Updated |
| Satellite Service boundary | Offline consumer of Suite Satellite Service | Strong separation; cache manifest and ingest-voting contract are required. | Medium. | Keep |
| 10 GB cache | Includes imagery, manifests, overviews, descriptors unless split | Plausible at 0.5 m/px with compression; 0.3 m/px plus descriptors may exceed unless pruned. | Medium. | Updated |
| Jetson Orin Nano Super | 67 TOPS INT8, 8 GB, 25 W | Official specs support the restriction; thermal throttling remains a risk. | Medium-high. | Keep |
| Test data gap | Sample imagery lacks IMU/ground truth | Public datasets help prototype, but final acceptance needs synchronized representative data. | High. | Updated |

## Key Findings

1. Use a hybrid estimator: VO/IMU for frame propagation, satellite/VPR anchors for absolute correction, ESKF covariance as the safety gate.
2. Do not run heavy VPR/re-ranking every frame; invoke it on cold start, VO failure, covariance growth, sharp turns, and disconnected segments.
3. Avoid GPL libraries in production dependencies unless the project accepts GPL obligations. GPL VIO/SLAM tools should be benchmarks or references, not selected production components.
4. The cache must be designed as imagery + metadata + descriptor index, not just raster tiles.
5. ArduPilot Plane SITL and representative camera+IMU data are blocking validation dependencies, but not blockers for solution drafting.

## Sources

See `_docs/00_research/01_source_registry.md` for the detailed source list.