gps-denied-onboard/_docs/02_document/glossary.md

Glossary

Status: confirmed-by-user Date: 2026-04-27 Scope: project-specific terminology only. Generic software / network / OS terms (REST, JSON, TCP, container, etc.) are intentionally excluded. Source convention: (source: <file> [§<section>]) — points back to the input where the term originates. (decision: 2026-04-27) marks terms whose meaning was locked during the Phase 2a.0 review.

---

A

• Absolute pose — position + orientation derived from a cross-view match against the satellite basemap (Component 3 + PnP). Synonym: visual fix, satellite-anchored fix, anchor fix. Distinguished from relative pose. (source: solution.md §Component 3)
• Active-conflict sector — operational sub-area where building destruction or major scene change is expected; drives stricter freshness budget (<6 months) and larger VPR top-K. (source: AC-8.2, AC-NEW-6)
• AGL — Above Ground Level (altitude reference). UAV mission profile is ≤1 km AGL. (source: restrictions.md §UAV & Flight)
• AI camera — operator-controllable mission camera with gimbal + zoom; output consumed by onboard AI detection systems. Distinct from the nav cam. Pose available to this build: gimbal angle + zoom only (not airframe bank/pitch). (source: restrictions.md §Cameras, AC-7.1)
• Airframe manifest — per-airframe signed configuration document produced by the Provisioning Tool (Component 12) at client setup. Contains FC firmware version, MAVLink2 signing-key fingerprint, sysid assignments (10/11), camera intrinsics, FC parameter pinning. (decision: 2026-04-27)
• Anchor fix — see absolute pose.
• ArduPilot — autopilot firmware. The only autopilot target in v1 scope. Configured with GPS1_TYPE=14 for MAVLink GPS injection. PX4 is out of v1 scope. (source: restrictions.md §Sensors & Integration; AC-4.3)
• Azaion Suite — the broader product family this build is one component of. Sibling components include Satellite Service, AI detection, semantic detection. (source: AC-8.1; decision: 2026-04-27)
• Azaion Suite Satellite Service — sibling Suite component responsible for upstream satellite imagery sourcing and onboard-tile ingest with 2-flight voting. Out of scope for this build except at the tile-cache folder boundary. Contract authorship lives in ../satellite-service/. (source: AC-8.1; decision: 2026-04-27)

B

• Basemap — the satellite reference imagery surface against which UAV nav-cam frames are matched. Stored as MBTiles z=19 in the local tile cache. (source: AC-NEW-7, solution.md §Tile generation; decision: 2026-04-27)
• Bench-off — comparative empirical measurement on Orin Nano Super @ 25 W against the dataset suite (AerialVL / UAV-VisLoc / AerialExtreMatch / 2chADCNN season set / TartanAir V2 / internal Mavic / first internal fixed-wing flight). Used to lock matcher / VO / VPR / z-level decisions. (source: solution.md §Component 3, §Component 4)

C

• Candidate pool — Service-side staging area for onboard-generated tiles awaiting 2-flight voting promotion. Companion writes here post-flight; Service ingest reads. (source: solution.md §Tile generation; AC-NEW-7)
• Companion computer — the Jetson Orin Nano Super running this build alongside the FC. Not the FC itself, not the GCS. (source: restrictions.md §Onboard Hardware)
• Companion-side FDR — slim flight log on the companion NVMe holding ONLY signals the FC dataflash does not capture (per-stage gate values, source-label decisions, tile-generation events, failure thumbnails, Jetson health). 3-flight rolling retention, ~500 MB/flight compressed. Distinct from the FC dataflash. (decision: 2026-04-27, supersedes AC-NEW-3 v1.0)
• Confidence score — (σ_xy, source_label) pair carried on every emitted fix. Cross-cutting (Component 11). (source: AC-1.4)
• Cross-view matching — matching a UAV nav-cam frame against a satellite basemap chunk to obtain an absolute pose. Cross-domain (aerial photo ↔ ortho satellite tile) — distinguished from frame-to-frame VO matching. (source: solution.md §Component 3)
• cuVSLAM — NVIDIA's CUDA-accelerated monocular+IMU VO/SLAM engine. v1 visual odometry (Component 4). Apache-2.0, drop-in via isaac_ros_visual_slam ROS 2 wrapper. (source: solution.md §Component 4; M-22, M-23)

D

• Dead reckoning — IMU-only position propagation when no visual fix is available. Source-label dead_reckoned. Performed FC-side by EKF3, never companion-side in v1. (source: AC-1.4, AC-5.2; M-26)
• DEM — Digital Elevation Model. SRTM-30 m DEM is loaded per-sector and consumed by Component 1b (Orthority) for orthorectification. (source: solution.md §Component 1b)
• DDS — middleware transport layer used by ROS 2 Humble. ~2–5 % CPU overhead accepted in exchange for isaac_ros_visual_slam + MAVROS integration. (source: solution.md §Component 9)

E

• EKF3 — ArduPilot's 24-state classical extended Kalman filter, runs at 400 Hz on the FC. The ONLY state-propagating filter in the v1 system. Consumes our GPS_INPUT plus its own IMU/baro/compass. (source: solution.md §Component 5; M-26)
• ESKF — Error-State Kalman Filter; tangent-space covariance on SO(3). Reserved for a hypothetical v1.x companion-side filter only — NOT used in v1. (source: solution.md §Component 5; S69)

F

• Failsafe — autopilot fallback to IMU-only dead reckoning when this build fails to emit a fix for >3 s. (source: AC-5.2; restrictions.md §Failsafe)
• FC — Flight Controller; the ArduPilot board on the airframe. (source: restrictions.md §Sensors & Integration)
• FC dataflash — ArduPilot's microSD-resident binary log on the FC itself. Authoritative for IMU traces, received GPS_INPUT frames, EKF3 internal state, MAVLink raw tlog. Companion-side FDR does NOT duplicate these. (decision: 2026-04-27)
• Failure thumbnail — low-rate (≤0.1 Hz) downsampled JPEG of nav-cam frames that failed tile generation. Forensic-only, retained on companion FDR for AC-NEW-7 audit. Other frames are NOT retained (no raw-frame storage policy). (source: AC-8.5, AC-NEW-3 revised)
• FDR — Flight Data Recorder. In this build refers to the companion-side FDR (slim, companion-side-unique signals only). Not to be confused with the FC dataflash. See Companion-side FDR. (source: AC-NEW-3 revised; decision: 2026-04-27)
• Fixed-wing — UAV airframe type (winged, not multirotor). The only airframe class in scope. (source: restrictions.md §UAV & Flight)
• Frame center — geographic center of a navigation-camera frame projected onto the ground. Primary AC-1.1 / AC-1.2 accuracy target. Synonym: photo center (problem.md uses "photo", AC uses "frame"). (source: problem.md, AC-1.1)
• Freshness budget — maximum allowable age of a satellite tile: <6 months for active-conflict sectors, <12 months for stable rear sectors. Tiles past budget are rejected or down-confidence-weighted. (source: AC-8.2, AC-NEW-6)

G

• GCS — Ground Control Station. In this build, only QGroundControl is supported. Mission Planner is not in scope. There is no Azaion-custom GCS service. (source: AC-6.1, restrictions.md §Sensors; decision: 2026-04-27)
• GPS_INPUT — MAVLink message ID used to inject the GPS-equivalent fix into ArduPilot. Carries h_acc, v_acc, vel_acc covariance. The single MAVLink output channel from this build to the FC in v1. (source: AC-4.3)
• GPS-denial — operational condition where real GPS is jammed, spoofed, or otherwise unavailable. The trigger condition for this build's promotion to FC primary GPS source. (source: problem.md, AC-NEW-2)
• GPS-Denied system / GPS-Denied stack — this build itself; the onboard companion-computer software stack. Synonyms: the build, companion-side software. (source: AC-8.1)
• GSD — Ground Sample Distance, in cm/px on the ground. Nav cam at 1 km AGL ≈ 12 cm/px. Basemap at z=19 ≈ 60 cm/px. Scale ratio (basemap GSD / nav-cam GSD) is the matcher's binding constraint. (source: restrictions.md §Cameras, AC-8.1; decision: 2026-04-27)

I

• Isaac ROS — NVIDIA's robotics middleware extensions on ROS 2 Humble. Provides isaac_ros_visual_slam for cuVSLAM integration. v1 orchestration platform alongside MAVROS. (source: solution.md §Component 9; Q6 → A)

J

• Jetson Orin Nano Super — the onboard processing platform. 67 TOPS sparse INT8, 8 GB shared LPDDR5 (CPU+GPU share the same pool), 25 W TDP. Runs JetPack 6 / Ubuntu 22.04. (source: restrictions.md §Onboard Hardware)
• Jetson UI — pre-flight web UI deployed on the Jetson companion, accessed by the operator via wired connection during pre-flight. Used for: drawing route + operational sector, triggering tile fetch from the Suite Satellite Service, running Provisioning Tool steps, walking through camera intrinsics calibration. Requires pre-flight internet. (decision: 2026-04-27)

L

• LiteSAM — purpose-built satellite↔aerial AVL matcher (S58, MDPI Oct 2025). Used in this build in three NON-inline roles: (a) re-localization fallback (cold start, σ_xy > 50 m, sharp turn after VO loss); (b) offline validation oracle; (c) distillation teacher for a future inline student model. NOT inline due to ~1.5–2 s/pair latency on Orin Nano Super. (source: solution.md §Component 3; M-24)

M

• Mahalanobis gate — outlier rejection mechanism in Component 5. Drops fix candidates whose innovation w.r.t. the cuVSLAM relative-pose prior exceeds a threshold derived from AC-NEW-4. NOT a state-propagating filter — pure gate. (source: solution.md §Component 5; M-26)
• MAVLink2 signing — per-link cryptographic signing on every companion ↔ FC link. Mandatory in v1. Per-airframe signing key written to FC FRAM via MAV_CMD_SETUP_SIGNING during Provisioning Tool bootstrap. USB connections bypass signing — bench-only. (source: solution.md §Component 6; R10)
• MAVROS — ROS 2 ↔ MAVLink bridge node. Owned by Component 9. Subscribes to FC RAW_IMU / SCALED_IMU / ATTITUDE; publishes our GPS_INPUT. (source: solution.md §Component 9)
• MAVSDK — high-level MAVLink library. Used in this build for general telemetry (sysid=10) only. Does NOT inject GPS_INPUT (no native API; that goes through pymavlink). (source: AC-4.3, restrictions.md §Sensors)
• MBTiles — SQLite-backed tile-storage container format. One file for the whole tile cache (not thousands of filesystem entries). Used by Component 1 for the persistent tile cache; opened with WAL + connection pool + transaction batching. (source: solution.md §Component 1)
• Mission YAML — per-mission configuration written by Jetson UI alongside the tile fetch. Contains operational area polygon, sector classes (active-conflict / stable rear), mission ID. One of three configuration scopes. (decision: 2026-04-27)

N

• Nadir — straight-down direction from the airframe. Nav cam is fixed nadir-pointing. (source: restrictions.md §Cameras)
• Nav cam / Navigation camera — fixed downward-pointing 20 MP APS-C camera (ADTi 20MP 20L V1). Consumed by this build for position estimation. NOT operator-controllable, NOT gimbaled. Distinct from the AI camera. (source: restrictions.md §Cameras)

O

• ODOMETRY — alternate MAVLink ExtNav channel (richer covariance, native yaw error, quality field). Intentionally disabled in v1 (Option A in M-30) due to ArduPilot EKF3 double-fusion bugs (#30076 / #32506). Re-enables in v1.1 once F-T9 SITL confirms PR #30080-class clean source-switching. (source: AC-4.3 v1 scope clause)
• Operational area — the pre-cached union of sector + transit corridor for a mission. Up to ~400 km² total. Cache is persistent across flights. (source: restrictions.md §UAV & Flight)
• Operator — the UAV pilot operating the mission. Responsible for: pre-flight tile fetch via Jetson UI, monitoring via QGC during flight, optional re-localization hints via QGC. Single human role; no co-operator distinction in v1. (source: restrictions.md, AC-6.2)
• Orthority — Python library used by Component 1b for per-frame orthorectification. Frame-camera model + GeoTIFF DEM. Pip-installable, MIT-class license. Documented fall-back: cv2.warpPerspective + bilinear DEM if F-T14 latency budget (≤50 ms/frame) is exceeded. (source: solution.md §Component 1b; M-27)
• Orthorectification / Ortho — projecting a nav-cam frame onto the basemap projection (EPSG:3857 z=19) using the camera model + per-sector DEM. Output is a basemap-aligned tile. (source: solution.md §Component 1b)

P

• PnP — Perspective-n-Point, the geometric step that turns matched 2D-3D correspondences (cross-view matcher output) into an absolute pose + covariance. (source: solution.md §Component 3)
• Provisioning Tool — Jetson-side provision-fc.py workflow that runs once at client setup. Does FC parameter pinning (GPS1_TYPE=14, EK3_SRC1_*, SERIAL2_*), MAVLink2 signing-key bootstrap, and a smoke-test (RAW_IMU rate + GPS_INPUT round-trip). Produces the per-airframe signed manifest. Component 12. (decision: 2026-04-27)
• pymavlink — low-level MAVLink Python library. Used in this build EXCLUSIVELY for GPS_INPUT injection (sysid=11). MAVSDK has no native GPS_INPUT API. (source: AC-4.3, M-6)

Q

• QGC / QGroundControl — the supported GCS software. Operator-side application running on a laptop or tablet, communicating with the FC via MAVLink. Receives a 1–2 Hz downsampled telemetry summary from the companion through the FC. NOT running on the companion. (source: AC-6.1, restrictions.md §Sensors; decision: 2026-04-27)

R

• Re-localization (re-loc) — the act of recovering an absolute pose after VO/cuVSLAM tracking loss. Triggers: cold start (AC-NEW-1), sharp turn (AC-3.2), disconnected segment (AC-3.3), σ_xy > 50 m, VO failure for ≥2 frames. VPR + LiteSAM are the re-loc workhorses; SP+LG inline matcher is invoked after VPR narrows the candidate set. (source: AC-3.3, AC-8.6, solution.md §Component 3)
• Relative pose — frame-to-frame pose increment produced by cuVSLAM. Distinguished from absolute pose (matcher + PnP). (source: solution.md §Component 4)
• ROS 2 Humble — middleware platform on JetPack 6 / Ubuntu 22.04. v1 orchestration target (Q6 → A, locked 2026-04-26). Replaces the draft01 "single Python asyncio process". (source: solution.md §Component 9; M-29)

S

• Sector — operational sub-area within the operational area. Two sub-types matter: active-conflict (stricter freshness, K=20 VPR top-K) and stable rear (relaxed freshness, K=5). Plus a separate terrain classification (flat / moderate / rugged) used by Component 1b. (source: AC-8.2, AC-NEW-6, solution.md §Component 1b)
• σ_xy / sigma_xy — 2D position uncertainty: the 95% covariance ellipse semi-major axis in meters. Carried on every emitted fix; gates Component 1b tile-generation eligibility (≤5 m hard, ≤3 m for full-quality writes). (source: AC-1.4, AC-NEW-7)
• SITL — Software-In-The-Loop ArduPilot simulator. Used by F-T9 to validate the full MAVLink loop (GPS_INPUT injection, source switching, MAVLink2 signing). (source: solution.md §F-T9)
• Source label — categorical tag on every emitted fix: satellite_anchored (matcher+PnP succeeded), vo_extrapolated (cuVSLAM continuation from last anchor), dead_reckoned (no recent visual fix). Drives FC's confidence treatment. (source: AC-1.4)
• Spoofing-promotion — the system action of promoting our estimate to FC primary GPS source when real GPS is detected as spoofed/lost. Latency target <3 s (AC-NEW-2). Driven by Component 7 watching GPS_RAW_INT, EKF_STATUS_REPORT, SYS_STATUS. (source: AC-NEW-2)
• Stable rear sector — operational sub-area where major scene change is not expected. Relaxed freshness budget (<12 months); smaller VPR top-K (K=5). Opposite of active-conflict sector. (source: AC-8.2)
• Suite Service ingest — server-side process at the Suite Satellite Service that consumes onboard-uploaded tiles via the candidate pool and applies 2-flight voting before promoting them to trusted basemap. Out of scope for this build (lives in ../satellite-service/). (source: AC-NEW-7)
• sysid (system ID) — MAVLink endpoint identifier. Companion uses two: 10 (MAVSDK telemetry) and 11 (pymavlink GPS_INPUT). FC uses its native SYSID_THISMAV. Routing handled by ArduPilot's native MAVLink routing — no mavlink-router daemon. (source: solution.md §Component 6; M-31)

T

• TartanAir V2 — synthetic dataset (Q4 → A, locked) used as early-stage matcher and VO baseline before real flight data is available. (source: solution.md, Q4)
• TensorRT (TRT) — NVIDIA's GPU inference compiler. All heavy NN inference in this build runs as TRT engines (FP16 default; INT8 where validated). Engines built at install time, not at first run, to meet AC-NEW-1 cold-start budget. (source: solution.md §Component 9, AC-NEW-1)
• Tile — slippy-XYZ z=19, 512×512 px, ~60 cm/px GSD. The unit of basemap storage in the tile cache. Decoupled from the VPR chunk (the unit of retrieval). Carries sidecar metadata: parent_pose_sigma_xy, terrain_class, trust_level, capture_date. (decision: 2026-04-27, supersedes z=20 in restrictions.md / solution.md)
• Tile cache — the persistent MBTiles store on the companion NVMe at /var/azaion/tile-cache/ (path TBD with Suite Service contract). Read+write during flight. ~700 MB for a 400 km² operational area at z=19. Persistent across flights — not redownloaded. (source: restrictions.md §Satellite Imagery; decision: 2026-04-27)
• Tile-cache folder — the boundary contract between this build and the Suite Satellite Service. Pre-flight: tiles arrive in this folder via the Service's fetch flow (out-of-scope mechanism). In-flight: this build reads + writes to this folder. Post-flight: this build's uploader pushes new tiles from this folder to the Service candidate pool. The folder layout / file naming is owned by ../satellite-service/. (decision: 2026-04-27)
• Trust level — sidecar metadata on each onboard-generated tile: candidate (default; σ_xy ≤ 5 m), soft (σ_xy ∈ (3, 5] m), or trusted-basemap (post Service-side 2-flight voting). Determines whether downstream flights match against it. (source: AC-NEW-7)
• TTFF — Time-to-First-Fix on cold start. Budget: <30 s from companion-computer boot to first valid GPS_INPUT (AC-NEW-1). Drives TRT engine pre-build, FAISS index pre-load, mmap-warm tile cache. (source: AC-NEW-1)

V

• Visual fix — see absolute pose.
• VO — Visual Odometry. Frame-to-frame relative pose. In v1 supplied by cuVSLAM in monocular+IMU mode. Distinguished from cross-view matching against the satellite basemap. (source: solution.md §Component 4)
• VPR — Visual Place Recognition. Global descriptor retrieval (DINOv2 SALAD/BoQ; AnyLoc fallback) over a FAISS IVF index of per-chunk descriptors. Narrows the basemap to a top-K candidate-chunk shortlist on re-localization triggers. Conditionally invoked, not per-frame. (source: solution.md §Component 2; AC-8.6)
• VPR chunk — ground-footprint-sized (~600–800 m at 1 km AGL, 40–50 % overlap) retrieval unit derived from the z=19 storage tile cache. Decoupled from the storage tile — must NOT be conflated. Multi-scale: fine-scale (z=19-derived) + coarse (z=17/z=18 effective scale) for change-robust retrieval in active-conflict sectors. (source: AC-8.6, restrictions.md §Satellite Imagery)

W

• WGS84 — coordinate system used for all output GPS coordinates. Matches GPS_INPUT spec. (source: AC-6.3)

Z

• z=19 / Storage tile zoom — slippy-XYZ zoom level 19, ~60 cm/px GSD, 512×512 tiles. The pinned basemap storage zoom for v1. Scale ratio to nav cam at 1 km AGL is 5× (above the 4× safety threshold quoted in solution.md draft03 §Component 1) — accepted as v1 default with documented fall-back to z=20 if matcher bench-off shows AC-2.2 (MRE <2.5 px cross-domain) failure. ~700 MB cache for a 400 km² operational area. (decision: 2026-04-27, supersedes restrictions.md §Satellite Imagery z=20 clause)