Topic

openroad.navigation.position

ZeroMQ transports the message as two frames: the UTF-8 topic followed by a JSON object.

Version

Schema version: 1

Units and conventions

All physical quantities use SI units. Geographic and angular quantities are expressed in radians rather than degrees. All defined fields are always present; unavailable values are JSON null.

Timestamp uses the common OpenRoadCode timestamp contract:

seconds: uint64 whole seconds since 1970-01-01T00:00:00 UTC
nanoseconds: uint32 fractional nanoseconds in the range 0..999,999,999

Message envelope

{
  "version": 1,
  "timestamp": {"seconds": 1787337000, "nanoseconds": 123456000},
  "source": "simulator",
  "data": {
    "latitude_rad": 0.74705,
    "longitude_rad": -1.44885,
    "altitude_m": 250.5,
    "fix_mode": 3,
    "satellites_visible": 14,
    "satellites_used": 10,
    "accuracy_m": 2.5,
    "is_cached": false
  }
}

Data fields

Field	JSON type	Unit / range	Nullable	Meaning
`latitude_rad`	number	rad, -pi/2..pi/2	yes	Geodetic latitude
`longitude_rad`	number	rad, -pi..pi	yes	Geodetic longitude
`altitude_m`	number	m	yes	Altitude reported by the source; signed values are allowed
`fix_mode`	integer	1, 2, or 3	yes	Source fix mode: no fix, 2D, or 3D
`satellites_visible`	integer	>= 0	yes	Satellites visible to the source
`satellites_used`	integer	>= 0	yes	Satellites used in the solution
`accuracy_m`	number	m, >= 0	yes	Position accuracy estimate supplied by the source
`is_cached`	boolean	true/false	no	True when the position is a retained/cached sample rather than a fresh observation

When both satellite counts are available, satellites_used must not exceed satellites_visible.

Position messages do not include speed or course. Those values belong to openroad.navigation.motion, documented in the Message Bus IDD. Older position examples containing speed_m_s or course_rad do not match the current encoder/validator; unknown data fields are rejected.

Service-local route playback uses source = "route-simulation" without changing the schema. Synthetic fix/accuracy/satellite values are development data, not evidence of an actual GNSS fix. The bridge continues producing real GPS while ORC temporarily publishes the route-generated position.

Producer requirements

Producers must publish every defined field, using null when a value is unavailable. Values must be finite JSON numbers and conform to the units and ranges above. Producers may originate from gpsd, browser geolocation, simulation, CAN/GNSS gateways, or other implementations; source identifies the producer without changing the topic semantics.

Consumer requirements

Consumers must validate the envelope and data contract before using a message. Consumers must tolerate null for every nullable field and must not infer a usable position solely from field presence. fix_mode >= 2 indicates a usable 2D or 3D fix when fix mode is supplied.

Versioning

Version 1 is the initial public position contract. Breaking semantic or structural changes require a new schema version. The topic remains the semantic identity of normalized geographic position state.