# Comparison Framework

## Selected Framework Type

Decision support with exact-fit component selection.

## Selected Dimensions

1. Required inputs/outputs and ownership boundaries
2. Operating context and lifecycle fit
3. Non-functional envelope fit: latency, memory, storage, thermal, safety
4. Licensing and deployability
5. Evidence quality and validation burden
6. Security and safety failure modes
7. Selection status

## Initial Population

| Component Area | Candidate | Option Family | Inputs / Outputs | Fit Summary | Status |
|----------------|-----------|---------------|------------------|-------------|--------|
| Calibration / geometry | OpenCV 4.x | Established production / open-source | image/object points -> intrinsics, distortion, homography, inlier mask | Exact utility fit; permissive production use. | Selected |
| VO / VIO | BASALT + project-owned safety/anchor wrapper | Open-source production candidate | nav frames + FC IMU/calibration -> relative VIO state; wrapper adds source labels, anchor fusion, calibrated confidence, and MAVLink semantics | Best production candidate after user decision: permissive license, strong benchmark evidence, and lower implementation burden than custom VIO. | Selected |
| VO / VIO | OpenVINS | Open-source research | monocular camera + IMU -> VIO state/covariance | Best covariance/reference story, but GPL-3 and generic VIO ownership make it a benchmark/reference rather than shipped core. | Reference only |
| VO / VIO | Kimera-VIO | Open-source production candidate / fallback | mono or stereo camera + IMU -> VIO/SLAM outputs | BSD-friendly, but heavier/stereo-oriented and mono-inertial path has documented parameter caveats. | Backup candidate |
| VO / VIO | OpenCV geometry + project-owned ESKF | Custom fallback | nav frames + FC IMU/attitude/altitude + satellite anchors -> relative motion, absolute updates, covariance, source labels | Fallback if BASALT fails project data/runtime tests; still needed as safety/anchor wrapper around any VIO library. | Fallback / wrapper |
| VO / VIO | ORB-SLAM3 | Open-source research | monocular/stereo/RGB-D + optional IMU -> SLAM pose | Useful benchmark; GPLv3, map runtime, and initialization complexity make it poor production dependency. | Rejected for production |
| Global retrieval | DINOv2-VLAD / AnyLoc-style descriptors | Current SOTA / research | image/chunk -> descriptor | Strong VPR evidence; trigger-only use due runtime/memory and TensorRT fidelity risk. | Selected with runtime gate |
| Vector retrieval | FAISS | Established production / open-source | descriptor matrix + query -> top-K IDs | Exact fit for offline VPR chunk retrieval. | Selected |
| Local matching | LightGlue + DISK/ALIKED | Current SOTA / open-source | two images -> keypoint correspondences/scores | Exact local-match interface; avoids SuperPoint license issue. | Selected with runtime gate |
| Local matching | SuperPoint + LightGlue | Current SOTA / known-bad/licensing caveat | two images -> matches | Technically good; licensing requires explicit review. | Needs user decision / fallback only |
| Cache imagery | COG + manifest + sidecars | Established geospatial format | georeferenced raster + metadata -> efficient local reads | Good immutable tile unit; generated tiles can be written as new COGs. | Selected |
| Cache packaging | PMTiles | Established web-map archive | tile pyramid -> single archive | Efficient reads, but read-only; not suitable for in-flight mutable writes. | Rejected for mutable cache |
| Estimator | Custom ESKF mode machine | Custom production | VO/IMU/VPR/GPS-health -> WGS84 state + covariance + label | Needed for source labels, covariance gates, blackout/spoofing behavior. | Selected |
| MAVLink integration | MAVSDK + pymavlink | Established APIs | telemetry in, `GPS_INPUT` out | MAVSDK handles telemetry; pymavlink handles raw `GPS_INPUT`. | Selected |
| FDR | PostgreSQL event index + CBOR payload segments with optional Parquet export | Established storage | frame estimates, IMU, MAVLink, health, tiles -> bounded replayable log | Matches project PostgreSQL choice while keeping compact append payloads. | Selected pattern |
| Validation | AerialVL + EuRoC + Plane SITL + representative flight | Multi-source test strategy | datasets/sim/flight -> AC evidence | Public data is partial; final representative data is mandatory. | Selected |

## Round 2 Decision Notes

- **OpenVINS vs custom OpenCV**: OpenVINS wins if the comparison is against a naive OpenCV-only VIO implementation. The selected design is not that; it is OpenCV geometry plus a product-owned estimator/state machine, with OpenVINS used as a benchmark/reference.
- **Satellite retrieval**: DINOv2-VLAD remains the best global candidate generator found, but aerial VPR sources require chunk scale/overlap tuning, dynamic top-K, and geometric verification.
- **Anchor verification**: ALIKED/LightGlue remains the preferred learned local matcher, while SIFT/ORB stays as a regression/fallback baseline and SuperPoint remains license-gated.

## Round 3 Decision Notes

- **User decision**: BASALT is selected as the production VIO candidate.
- **Confidence/covariance**: OpenVINS remains the covariance/reference baseline because its EKF exposes clearer uncertainty semantics than BASALT/Kimera.
- **Nadir support**: no compared VIO library has a special fixed-wing nadir mode; the acceptance path is calibration, altitude/scale constraints, satellite anchors, and representative replay validation.

## Baseline Alignment

- "Position estimate" means WGS84 frame center emitted to FC plus a 95% covariance semi-major axis and source label.
- "Satellite anchored" means a visual match passed VPR retrieval, local matching, RANSAC, freshness, covariance, and Mahalanobis gates.
- "Normal flight segment" means the AC-2.1a conditions, not turns/blackout/stale imagery.
- "Selected with runtime gate" means the API capability fits, but final deployment depends on Jetson profiling against AC-4.1 and AC-4.2.