DPT third field depends on nmea version?

[aldas]

DPT documentation refers to https://gpsd.gitlab.io/gpsd/NMEA.html#_dpt_depth_of_water and in that is example $INDPT,2.3,0.0*46

that example is not parseable by the library. I get nmea: INDPT invalid range scale: index out of range

Some other documents ala https://www.tronico.fi/OH6NT/docs/NMEA0183.pdf describe DPT as

or https://www.eye4software.com/hydromagic/documentation/nmea0183/ as Example: $SDDPT,3.6,0.0*52

It would be nice if DTP parsing can handle 2 and 3 fields gracefully without erroring.

[icholy]

@aldas what sensor is outputting those sentences?

[aldas]

Well, I am writing diagnostics software to read some echosounder values. At first we intent to use "Skipper FDS-101 Echosounder" which uses 3 fields in DPT but when writing software I saw this inconsistency when writing unit-tests against spec + manual examples. Vessels that we deal with have wide range of electronics and god knows when it would 3 fields and when 2 fields.

From googling it seems that these 2 field ones do exist https://forum.arduino.cc/t/nmea-depth-sensor/267009 $SDDPT,004.8,*75

[icholy]

Thanks for the details, we'll get this fixed for you. If you're short on time, you can unblock yourself by registering a custom parser for the DPT sentences https://github.com/adrianmo/go-nmea#custom-message-parsing

err := nmea.RegisterParser("DPT", func(s nmea.BaseSentence) (nmea.Sentence, error) {
    p := nmea.NewParser(s)
    p.AssertType(TypeDPT)
    dpt := DPT{
    BaseSentence: s,
    Depth:        p.Float64(0, "depth"),
    Offset:       p.Float64(1, "offset"),
    }
    if len(p.Fields) > 2 {
    dpt.RangeScale = p.Float64(2, "range scale")
    }
    return dpt, p.Err()
})
if err != nil {
    panic(err)
}