Re: altitude validity

[Greg Troxel]

Thanks.  This is about direwolf, a software modem for amateur radio packet.

So this notion of NaN makes a lot of sense, but it was unobvious from
reading gps.h and from reading the libgps man page.

I am also unclear on that ALTITUDE_SET means, if one is supposed to
check against NaN.

"Gary E. Miller" <address@hidden> writes:

>> 2A) This means therefore that if a receiver provides one of altHAE or
>> altMSL, but not the other, gpsd will use its own geoid model to
>> compute the other, and thus the user gets both or none.
>
> Usually.  Or maybe libgps connected to an old gpsd and only got
> altitude.

good point.

>> 3) Someone who wants normal-people-altitude, sort of "WGS84 height
>> above geoid" or (NA only) "NAVD88, ish" would want to say
>>     if API >= 9
>>        read altMSL
>>     else
>>       read altitude
>>     endif
>
> Or maybe:
>
>      if altMSL != NAN
>         read altMSL
>      else if altitude != NAN
>         read altitude
>      else
>         NAN
>      endif

But altMSL is only present with API level 9.0 or higher.  So you can't
write code like that; you have to ifdef on API level to reference it.
I feel like I must be missing something.

> Except altitude may be MSL, may be HAT, or may be garbage.  I deprecated it
> because it was random.

ok