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GPS-Denied Onboard Localization — System Flows

Flow Inventory

# Flow Name Trigger Primary Components Criticality
F1 Pre-flight cache preparation Operator sync before mission Satellite Service, cache/tile lifecycle, satellite retrieval High
F2 Normal frame processing Navigation frame + FC telemetry Camera ingest, BASALT VIO adapter, safety/anchor wrapper, MAVLink, FDR High
F3 Satellite relocalization Cold start, VO failure, sharp turn, covariance growth, stale anchor Satellite retrieval, anchor verification, safety/anchor wrapper High
F4 Visual blackout / spoofing degraded mode Image-quality failure and GPS health failure Camera ingest, MAVLink telemetry, safety/anchor wrapper, QGC, FDR Critical
F5 Generated tile lifecycle High-confidence pose + usable frame Camera ingest, safety/anchor wrapper, cache/tile lifecycle, FDR Medium
F6 Post-flight sync and audit Landing / operator offload Cache/tile lifecycle, Satellite Service, FDR Medium
F7 Validation replay Test harness invocation Validation harness, system runtime, public datasets, SITL High

Flow Dependencies

Flow Depends On Shares Data With
F1 Satellite Service cache export F2, F3, F5
F2 F1 for cache availability; FC telemetry F3, F4, F5, FDR
F3 F1 cache/index; F2 state estimate F2, F5
F4 F2 telemetry and quality signals F2, QGC/FDR
F5 Accepted state/covariance from F2/F3 F6
F6 F5 generated tiles and FDR Satellite Service
F7 Test fixtures and selected execution environment All flows

Flow F1: Pre-Flight Cache Preparation

Description

Before flight, the Satellite Service provides an offline cache for the operational area, including COG tiles, manifests, sidecars, VPR chunks, descriptors, and FAISS index files.

Preconditions

  • Operational area and sector freshness classification are known.
  • Cache imagery meets 0.5 m/px minimum and ideally 0.3 m/px.
  • Cache package fits storage budget or has approved split descriptor budget.

Sequence Diagram

sequenceDiagram
    participant Operator
    participant SatelliteService
    participant CacheLifecycle
    participant SatelliteRetrieval

    Operator->>SatelliteService: Request mission cache
    SatelliteService-->>CacheLifecycle: COG tiles + manifests + sidecars
    CacheLifecycle->>CacheLifecycle: Verify signatures, hashes, freshness, resolution
    CacheLifecycle->>SatelliteRetrieval: Load VPR chunks + FAISS index
    CacheLifecycle-->>Operator: Cache validation report

Data Flow

Step From To Data Format
1 Satellite Service Cache lifecycle Tiles and metadata COG + PostgreSQL/PostGIS manifest + signed JSON sidecars
2 Cache lifecycle Satellite retrieval Descriptor/index files FAISS index + descriptor sidecars
3 Cache lifecycle Operator/FDR Validation report Markdown/CSV/log

Error Scenarios

Error Where Detection Recovery
Stale tile Cache validation Capture date exceeds sector threshold Reject/down-confidence tile
Hash mismatch Cache validation Sidecar hash mismatch Reject tile and report security event
Cache too large Cache load Storage accounting > budget Require cache rebuild or approved split budget

Performance Expectations

Metric Target Notes
Runtime network calls 0 No in-flight provider calls
Cache load Within cold-start budget contribution Exact threshold set during implementation

Flow F2: Normal Frame Processing

Description

During normal flight, the system processes each navigation frame and FC telemetry sample. The camera component first checks for total occlusion/blackout. Usable frames go to BASALT VIO; total-occlusion frames bypass VIO and send the wrapper into IMU-only degraded propagation.

Preconditions

  • Camera calibration/extrinsics are loaded.
  • BASALT and wrapper are initialized.
  • FC telemetry stream is healthy.

Sequence Diagram

sequenceDiagram
    participant CameraIngest
    participant FCTelemetry
    participant BasaltAdapter
    participant SafetyWrapper
    participant MavlinkOutput
    participant FDR

    CameraIngest->>CameraIngest: Total occlusion / blackout check
    CameraIngest->>BasaltAdapter: Usable frame + timestamp + calibration
    CameraIngest-->>SafetyWrapper: Degradation signal if total occlusion
    FCTelemetry->>BasaltAdapter: IMU/attitude/altitude
    BasaltAdapter-->>SafetyWrapper: Relative VIO state + quality
    SafetyWrapper->>SafetyWrapper: Calibrate covariance + source label
    SafetyWrapper-->>MavlinkOutput: GPS_INPUT estimate
    SafetyWrapper-->>FDR: Estimate + inputs + health

Data Flow

Step From To Data Format
1 Camera ingest BASALT adapter or safety wrapper Frame metadata, image, occlusion status Frame DTO / DegradationSignal
2 FC telemetry BASALT adapter IMU/attitude/altitude MAVLink-derived telemetry DTO
3 BASALT adapter Safety wrapper Relative VIO state VioState DTO
4 Safety wrapper MAVLink output WGS84 estimate GPS_INPUT
5 Safety wrapper FDR Inputs/outputs/audit FDR segment event

Error Scenarios

Error Where Detection Recovery
Total occlusion / blackout Camera ingest Occlusion status, exposure/texture/decode checks Bypass BASALT, enter IMU-only dead_reckoned propagation
Frame unreadable Camera ingest Decode/quality failure Mark visual signal degraded and bypass BASALT for that frame
VIO quality low BASALT adapter Tracking/completion metrics Trigger relocalization or dead reckoning
Covariance grows Safety wrapper Covariance threshold Degrade fix type/source label

Performance Expectations

Metric Target Notes
End-to-end latency <400 ms p95 Frame input to emitted estimate
Dropped frames <=10% sustained Under load
Memory <8 GB shared Jetson limit

Flow F3: Satellite Relocalization

Description

When the state becomes uncertain or disconnected, the system retrieves satellite/cache candidates and accepts an anchor only after local verification and safety gates pass.

Preconditions

  • Offline VPR chunks and FAISS index are loaded.
  • Trigger condition is met: cold start, VO failure, sharp turn, disconnected segment, covariance growth, or stale anchor.

Sequence Diagram

sequenceDiagram
    participant SafetyWrapper
    participant SatelliteRetrieval
    participant AnchorVerification
    participant CacheLifecycle
    participant FDR

    SafetyWrapper->>SatelliteRetrieval: Relocalization request
    SatelliteRetrieval->>CacheLifecycle: Read candidate chunk metadata
    SatelliteRetrieval-->>AnchorVerification: Top-K candidates
    AnchorVerification->>AnchorVerification: ALIKED/DISK+LightGlue + RANSAC
    AnchorVerification-->>SafetyWrapper: Accepted/rejected anchor
    SafetyWrapper->>SafetyWrapper: Mahalanobis + freshness + provenance gates
    SafetyWrapper-->>FDR: Anchor decision audit

Data Flow

Step From To Data Format
1 Safety wrapper Satellite retrieval Query frame and prior/covariance Relocalization DTO
2 Satellite retrieval Anchor verification Top-K chunks Candidate list
3 Anchor verification Safety wrapper MRE, inliers, homography, provenance AnchorDecision DTO

Error Scenarios

Error Where Detection Recovery
No good candidate Retrieval/verification Low score or failed RANSAC Continue degraded and request GCS hint after threshold
Stale candidate Cache lifecycle Capture date gate Reject/down-confidence
Implausible anchor Safety wrapper Mahalanobis/impossible velocity gate Reject and log

Performance Expectations

Metric Target Notes
Invocation frequency Trigger-based only Not per-frame
Cross-domain MRE <2.5 px for accepted anchors AC-2.2

Flow F4: Visual Blackout / Spoofing Degraded Mode

Description

When visual localization is unavailable due to total occlusion/blackout and GPS is denied/spoofed, the wrapper switches to honest IMU-only propagation from the last trusted state and degrades MAVLink output based on covariance/time thresholds.

Preconditions

  • Last trusted state exists.
  • FC telemetry continues.

Sequence Diagram

sequenceDiagram
    participant CameraIngest
    participant FCTelemetry
    participant SafetyWrapper
    participant MavlinkOutput
    participant QGC
    participant FDR

    CameraIngest-->>SafetyWrapper: Total occlusion / visual blackout signal
    FCTelemetry-->>SafetyWrapper: GPS health/spoofing signal
    SafetyWrapper->>SafetyWrapper: IMU-only propagation + monotonic covariance growth
    SafetyWrapper->>SafetyWrapper: Switch source_label to dead_reckoned
    SafetyWrapper-->>MavlinkOutput: Degraded GPS_INPUT
    SafetyWrapper-->>QGC: VISUAL_BLACKOUT_IMU_ONLY / FAILSAFE
    SafetyWrapper-->>FDR: Blackout and spoofing audit events

Error Scenarios

Error Where Detection Recovery
Blackout >30 s Safety wrapper Timer threshold Emit no-fix/failsafe
Covariance >500 m Safety wrapper Covariance threshold fix_type=0, horiz_accuracy=999.0
Spoofed GPS recovers Safety wrapper FC health + visual consistency gate Re-enable only after required stable interval and visual/satellite consistency

Performance Expectations

Metric Target Notes
Mode transition <=1 processed frame or <=400 ms AC-3.5
QGC status 1-2 Hz Downsampled operator awareness

Flow F5: Generated Tile Lifecycle

Description

When pose confidence is strong enough, the system orthorectifies navigation imagery into write-new generated tiles and records quality/provenance sidecars.

Preconditions

  • Parent pose covariance passes tile-write gate.
  • Frame quality supports orthorectification.

Data Flow

Step From To Data Format
1 Safety wrapper Cache lifecycle Pose/covariance + frame metadata TileGenerationRequest
2 Cache lifecycle Local storage Generated COG + sidecar COG + signed JSON
3 Cache lifecycle FDR Tile write event FDR event

Error Scenarios

Error Where Detection Recovery
Parent covariance too high Safety wrapper Sigma gate Do not write tile
Duplicate sector Cache lifecycle Spatial deduplication Keep latest/highest-quality tile
Sidecar write failure Cache lifecycle I/O error Log and do not mark tile eligible

Flow F6: Post-Flight Sync And Audit

Description

After landing, generated tiles and FDR evidence are exported for Satellite Service ingest and incident analysis.

Data Flow

Step From To Data Format
1 Cache lifecycle Satellite Service Generated tile package COG + sidecar + manifest delta
2 FDR Operator/audit tools Mission replay evidence Segmented logs + optional Parquet export

Error Scenarios

Error Where Detection Recovery
Upload unavailable Post-flight sync Network/service failure Retain package for retry
Candidate rejected by Service voting Satellite Service Ingest rules Keep as candidate/soft trust, not trusted basemap

Flow F7: Validation Replay

Description

The validation harness runs deterministic still-image, public dataset, SITL, Jetson, and representative replay scenarios against public interfaces.

Preconditions

  • Test data and expected results are pinned.
  • Execution mode is selected: Docker/replay and local Jetson hardware.

Data Flow

Step From To Data Format
1 Validation harness Runtime Images/telemetry/cache fixtures File/stream/MAVLink
2 Runtime Validation harness GPS_INPUT/FDR/status MAVLink/log files
3 Validation harness Reports Pass/fail metrics CSV/Markdown

Performance Expectations

Metric Target Notes
PR smoke <=15 min Still-image/cache/SITL subset
Release gate Hardware-dependent Jetson and representative replay required
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