[aprssig] Packet Interpretation - Wind or Motion

[Pierre Thibaudeau]

P.S.

I suspect that many (most) weather station software that are generating 
APRS data are actually sending wind speed in mph. Another compelling 
argument to re-write the spec with regard to DIR/SPD.

'73 - Pierre
__

Pierre Thibaudeau
VA2RKA/VA2RKB/VE2RIO/VE2RVR/VE2RQF/VE2RTO/VE2LKL/VE2TXD sysadmin

Today, 07:55 -0400, Pierre Thibaudeau wrote:

>    Today, 07:20 -0400, Lynn W. Deffenbaugh (Mr) wrote:
>    
>    >    To start a new topic in the group,
>    >    
>    >    As most of you know, I'm working on a new APRS-IS client.  I'm working on
>    >    improving my parser to parse, buffer, and display more datatypes coming in
>    >    over the APRS-IS stream and I've just started looking at weather packets.
>    >    I've stumbled across a station that appears to be moving (using @ position
>    >    updates) with a course and speed (CSE/SPD), but when looking at the comment
>    >    text visually, it more appears to be a weather packet wherein the CSE/SPD
>    >    should be the wind direction and speed.
>    >    
>    >    Any guidance on how to interpret these packets from K3YJP-4?
>    >    http://aprs.fi/?c=raw&call=K3YJP-4
>    
>    It is indeed a weather report; see APRS 101.
>    
>    Chapter 7 (p.27) specifies the DIR/SPD and later in Chapter 12 the section 
>    "Complete Weather Reports with Timestamp and Position" describes all the 
>    fields in such a message (explanation for the other fields after the 
>    DIR/SPD are given on the previous page, with "Positionless Weather Data".
>    
>    It must me noted that (to open yet another debate) the APRS specifications 
>    specifies that (in this format) wind speed is in knots and gust speed is 
>    in mph. However, APRS clients like findu.com, aprs.fi, UI-View are all 
>    interpreting the wind speed in mph (altough they all interpret the speed 
>    of moving objects in knots). Xastir on his part is "correctly" 
>    interpreting wind speed in knots. It drives me crazy as I "have" to create 
>    weather reports for APRS clients that do not follow the spec, even if it 
>    means that my APRS client of choice displays incorrect data.
>    
>    Note that for positionless weather reports, wind speed is expressed in 
>    mph. But discrepencies like this are to be expected. As mentioned in APRS 
>    101:
>    
>       "For historical reasons there is some lack of consistency between units 
>        of data in APRS packets — some speeds are in knots, others in miles 
>        per hour; some altitudes are in feet, others in meters, and so on. It 
>        is emphasized that this specification describes the units of data as 
>        they are transmitted on-air. It is the responsibility of APRS 
>        applications to convert the on-air units to more suitable units if 
>        required."
>    
>    With UI-View beeing in a frozen state, the spec should probably be revised 
>    (and Xastir and others be "fixed").
>    
>    '73 - Pierre
>    __
>    
>    Pierre Thibaudeau
>    VA2RKA/VA2RKB/VE2RIO/VE2RVR/VE2RQF/VE2RTO/VE2LKL/VE2TXD sysadmin