GNSS positioning, jump filtering and time update

Model status: confirmed; route navigation does not belong to this model

Input and output contract

The structural dependency of LocationService directly reveals the processing chain:

NmeaParser
  → GpsJitterFilter
  → LocationFix
  → ILocationEventSink
  → ITimeAuthorityUpdater

Only latestFix(LocationFix&) is exposed to the outside world. This means that pages, teams, and tracks should each not re-parse NMEA or bypass filters to read driver status.

Process a GNSS input

sequenceDiagram
  participant Driver as GNSS bytes
  participant Service as LocationService
  participant Parser as NmeaParser
  participant Filter as GpsJitterFilter
  participant Events as ILocationEventSink
  participant Time as ITimeAuthorityUpdater
  Driver->>Service: onGnssBytes(bytes, len, now_ms, last_motion_ms)
  Service->>Parser: parse NMEA revisions
  Service->>Filter: evaluate new fix
  Service->>Events: publish accepted location change
  Service->>Time: submit new time revision

Explicitly existing state

latest_fix_: The last LocationFix saved by the service.
last_fix_revision_: Avoid processing the same fix revision repeatedly.
last_time_revision_: Avoid processing the same time revision repeatedly.
reset(): Clear service status.

"Valid/Stale/NoFix" is a useful analysis language, but the current LocationService header file does not expose such a set of state machines; the original text writes it as confirmed state machine, which is an over-explanation. Drill-down plots now clearly differentiate between code facts and analysis projections.

The real boundary of time update

The ITimeAuthorityUpdater port clearly exists in the code; the document should read "LocationService submits updates to the time authority", and cannot be used to create a domain entity named GNSS Time Authority.

Content that does not belong here

Route, RouteLeg, along-route progress and yaw policy are not properties of LocationFix. The yaw rule currently resides in gps_page_runtime.cpp, indicating that the Navigation model is missing; it should remain in the Review Queue.

Drilldown and Evidence

LocationFix Lifecycle: Facts and Inferences
modules/core_gps/include/gps/domain/location_fix.h
modules/core_gps/include/gps/usecase/location_service.h
modules/core_gps/src/usecase/location_service.cpp
modules/core_gps/tests/test_location_service.cpp

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