> "status":0,
> "status_text":"Under way using engine",
> ...,
> "speed":0,
> ...,
> "course":0,
> "heading":511,
> ...}
>
> heading 511 indicates not available
> Maybe the status should be 15 = undefined = default?
Just chiming in as someone who deals interpreting with AIS data. Note that the 'Navigational Status' field is just reflecting what the underlying AIS message contains - gpsd is (correctly) not trying to alter it, but just pass through the data received. You should not assume 'under way using engine' means 'must be moving', which seems to be the underlying misunderstanding here. Ships will temporarily stop, and humans will forget to change it to 'at anchor' or 'moored' as well. (The primary difference is really only in the frequency of the messages sent).
In general, AIS data has a lot of human inputs, which means that any data pipeline that receives it needs to be especially liberal in what it accepts, and to do some sanity checking of its own before determining what is valid data to act on. These judgement calls will differ by use case, and I would not expect gpsd to be trying to do it. You'll also need to expect and validate/reject non-nonsensical data in the cases where you care; there is only very basic check-summing of the messages, and some will inevitably slip through (e.g, shiptype 8440) .
If you just want a (mostly) clean flow of well-structured and validated ship position data for an area of interest, there are commercial services which will provide this for you, taking out most of this hassle, but at a price. Depending on what your interest & area of expertise is, this may be a better solution.