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Publish GPS as foxglove.LocationFix messages on one channel of their own, e.g. /gnss/fix. The channel is found by its schema and needs no overlay declaration.
  • Fixes are timed by their MCAP log_time, like signals.
  • Publish only valid fixes. Drop a fix rather than send NaN or out-of-range values. A fix at exactly 0, 0 is always discarded, because that is what an unset protobuf field decodes to.
  • Publish one fix channel. With several, the first by topic name is used and the others are ignored with a warning.
  • A usable track needs at least two valid fixes at or after the first video frame. Fixes are kept at up to 10 per second.
  • When the position is derived rather than measured (e.g. from a map-frame pose and a georeference), say so in the overlay’s free-form source object, e.g. "source": {"gps": "derived_from_ego_pose"}. The message itself has no provenance field.
Do not publish latitude and longitude as signals. They are accepted as signals, but they do not form a GPS track.