Re: [gpsd-users] Communicating NMEA to gpsd as if my software was a GPS device

[Ellon Paiva]

Yo Gary!

On 9/4/19 9:09 PM, Gary E. Miller wrote:
> I looked at your sample file some more.  I thought you would like to
> know how wrong some of your "NMEA" is.

Yes!

> For example:
>
> $GPGGA,103642.879013,4850.432180742773,N,226.381659556439,E,7,08,,0,M,0,M,,*73
>
> Field 1, time of measurement: 103642.879013
> NMEA only allows 2 digits past the decimal point.  Some GPS use 3.
>
> Field 2, latitude: 4850.432180742773
> NMEA only allows 2 digits past the decimal point.  Some GPS use 3 or 4.
>
>
> Field 4, longitude: 226.381659556439
> Seriously, 226 degrees east?  NMEA range is +/- 180.

Oops, thanks for spotting this!

> NMEA only allows 2 digits past the decimal point.  Some GPS use 3 or 4.

OK, thanks for the info about the number of digits past the decimal point.

> Field 10, HDOP.  Missing.

This was in purpose, as I am not really simulating localization from 
satellites. Should I put a value, like one of this table here ? 
https://en.wikipedia.org/wiki/Dilution_of_precision_(navigation)#Meaning_of_DOP_Values[citation_needed]

> Field 11, altitude: 0
> Missing decimal point.

Thanks!

> Field 13, geoid separation: 0
> Zero?  Really???

Yeah, Really. :-) I based myself in the formula h = H + N, and that 
altitude means H and geoid separation means N. Since I only have z 
height ("h" in the formula), I thought it was doable to leave geoid 
separation as zero and set altitude to my z height. It seems I got the 
right value on the gpsd json output.

Maybe I could try to use proj4 to recover the undulation given a certain 
lat/lon and fill this field properly?

> Missing decimal point.
>
> Other sentences similarly non-compliant...
>
> These will make a good example of things gpsd should detect and
> complain about.

Thanks for looking at these logs!

At the end I'm not sure these would disturb gpsd. The safe_atof() on 
gpsutils.c seems to handle many decimal digits (I think it accepts a 
number to up 18 digits). About the missing fields, it seems that they 
are just not informed to gpsd clients, which would be a problem if the 
clients expect them, but I think that's not my case...

Best,

Ellon