[aprssig] Is floating point telemetry allowed in APRS?

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Mar 27 15:46:32 CDT 2013


His position packet says:

WA3NOA-RI>APRX21,qAR,WA3NOA-5:!4000.51NR07537.36W& WA3NOA Rx-only iGate 
and Digi

According to http://www.aprs.org/aprs11/tocalls.txt APRX21 is "APRXxx  
<39 for OH2MQK's RX-igate", so that'd be the software that is likely 
generating the out-of-spec packets.

Note also that the javAPRSSrvr t/t (type telemetry) filter will not pass 
any out-of-spec telemetry packets like these with floating point values 
or any that exceed 255.

Chapter 4 of aprs101.pdf describes the AX.25 Destination Address field.  
RXTLM-2 is not an application identifier (doesn't start with AP), nor 
anything else specifically described, so it's an alternate network 
identifier.  An SSID on the Destination Address, the -2 in this example, 
is an alternate way of specifying WIDE2-2 as the path, but I'm not sure 
if any digipeaters actually implement this.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 3/27/2013 4:32 PM, Andrew P. wrote:
> Whoops. I take that back. Here's a local guy near my house doing it.
>
> WA3NOA-RI>RXTLM-2,TCPIP,qAR,WA3NOA-5:T#043,0.2,0.0,1.0,0.0,0.0,00000000
>
> By the way, what's the RXTLM destination code for? I'll have to ask him (he's in my local ARES group).
>
> Andrew Pavlin, KA2DDO
> ------Original Message------
> From: Steve Dimse
> To: aprssig at tapr.org
> Sent: Mar 27, 2013 4:09 PM
> Subject: Re: [aprssig] Is floating point telemetry allowed in APRS?
>
>
> The spec is not fluid that way. If it says telemetry should look like
>
> T#005,199,000,255,073,123,01101001
>
> sending
>
> T#005,199.1,000,255,073,123,01101001
>
> is not within the spec, and many parsers will reject the packet outright, others might truncate, still others might crash. The results are undefined and therefore should not be used. The whole point of the spec was to have data that everyone could understand in the same way.
>
> People that have non-standard needs are supposed to use the user-defined part of the spec which allows for any data one might need without causing problems in other parsers.
>
> Can you give an example of such a packet?
>
> Steve K4HG
>
>
>
> On Mar 27, 2013, at 4:01 PM, Charles Blackburn wrote:
>
>> that is a good question, although i would assume that you could just drop the fraction and be done with it.
>>
>> charlie
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