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ZL3AI > APRDIG 23.12.03 19:29l 239 Lines 9110 Bytes #999 (0) @ WW
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To : APRDIG@WW
Subject: Re: GPGGA with no GPRMC?
From: Jeff King <jeff@aerodata.net>
Date: Fri, 19 Dec 2003 13:23:59 -0500
X-Message-Number: 22
The old Trimble SV6's (or something like that) did not have the RMC
sentences. But they are from 1995, and not very good, so I suspect not to
many are still around.
--
Jeff King, jeff@aerodata.net on 12/19/2003
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Subject: Re: GPGGA with no GPRMC?
From: Bob Bruninga <bruninga@usna.edu>
Date: Fri, 19 Dec 2003 13:56:11 -0500 (EST)
X-Message-Number: 23
On Fri, 19 Dec 2003, Scott Miller wrote:
>Are there any GPS units out there that send GPGGA but not GPRMC, or vice
>versa? I was looking over my code, and the way it's set up now it has to
>get both or it won't ever beacon at all. It obviously can't get full data
>without both, but do I need to provide an option to transmit with only one
>or the other?
Yes, certainly. APRSdos does this in descending priority:
If RMC is available it gets LAT/LONG/CSE/SPEED and sends it.
If GGA is available it gets LAT/LONG/Altitude and sends it.
If GLL is available it gets LAT/LONG **AND** it buffers it for 3 seconds
If VTG is available ** AND** there is a buffered GLL, then it combines
the GGA and VGA Course and SPeed and then sends a complete report
If GLB or RMZ then it takes altitude from those...
If HTM is availaable it takes the Heading (a magnetic compass)...
This makes APRSdos compatible with ALL gps units including LORAN...
The GLL/VTG combination was an absollute necessity back in the early
90's... but this buffering data for 2 seconds and combining data was not
done by some other APRS clients and it explains why some of those programs
didnt display CSE and Speed on some of the early trackers either...
The above list is from memory, so I hope I remembered them right...
de WB4APR
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Subject: Re: UNPROTO, etc.
From: Bob Bruninga <bruninga@usna.edu>
Date: Fri, 19 Dec 2003 13:59:38 -0500 (EST)
X-Message-Number: 24
On Fri, 19 Dec 2003, James Jefferson wrote:
>>Okay, let me ask it in a different way... My tracker shows up on
>>Findu and APRSworld when I use "APRSxx VIA WIDE, WIDE" and also when I
>>use "GPS VIA WIDE,WIDE".
>
>The APRSXX or APD215 are encoding software version numbers in the TOCALL
>field. Pretty much worthless, especially in the case of WinAPRS which encodes
>its version 3 times in some packets.
Eye of the beholder.... The TOCALL is extremely valuable to many people..
>Look on Bob B's site for a listing of the tocalls. You can also do stuff
>like ALTNET's or MIC-E encode latitude...
>
>>So what's the difference? Why should I use one construct instead of
>>the other? And why do I seem to see even stranger things (e.g.,
>>"APD215") when I look at raw packets on Findu? What do those mean??
>
>You can look in the APRS spec for further details, but it's not really that
>important for a "dumb" tracker.
If it is a dumb tracker then the GPSxx construct is the only way for it to
indicate its ICON type. Again, quite valuable...
de WB4APR, Bob
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Subject: Re: GPGGA with no GPRMC?
From: Bob Bruninga <bruninga@usna.edu>
Date: Fri, 19 Dec 2003 14:03:37 -0500 (EST)
X-Message-Number: 25
>The old Trimble SV6's (or something like that) did not have the RMC
>sentences. But they are from 1995, and not very good, so I suspect not to
>many are still around.
Yes, But the last thing we want is for "APRS" software to be selectively
ignoring many of our older trackers just for the programmers convenience.
All of thse are supposed to be supported in "APRS" programs:
GGA,RMC,GLL,VTG as a minimum and optionally GLB,RMZ and HDM
In fact, NMEA 0183 shows these as required I think also...
Bob
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Subject: Re: GPGGA with no GPRMC?
From: "Curt, WE7U" <archer@eskimo.com>
Date: Fri, 19 Dec 2003 11:08:14 -0800 (PST)
X-Message-Number: 26
On Fri, 19 Dec 2003, Jeff King wrote:
>The old Trimble SV6's (or something like that) did not have the RMC
>sentences. But they are from 1995, and not very good, so I suspect not to
>many are still around.
Correct. Never underestimate the thrifty ham! I have four of these
units in my hands. They put out GPGGA and GPVTG sentences.
-----------------------------------------------------------------
Curt, WE7U archer@eskimo.com
Arlington, WA, USA http://www.eskimo.com/~archer
"Lotto: A tax on people who are bad at math." -- unknown
"Windows: Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me: I picked the coordinate system!"
----------------------------------------------------------------------
Subject: Re: GPGGA with no GPRMC?
From: Jeff King <jeff@aerodata.net>
Date: Fri, 19 Dec 2003 14:40:42 -0500
X-Message-Number: 27
Maybe, but I suspect Scott is asking because of his OpenTrack tracker he is
working on. There are only so many boatanchors you can drag along, and the
fewer he drags along, IMHO, the better the protocol will be.
BTW, I suspect he is still thinking about making it open source, and that is
the beauty of open source, if you have a boat anchor you want it to work on,
then you just code it up yourself.
--
Jeff King, jeff@aerodata.net on 12/19/2003
On Fri, 19 Dec 2003 14:03:37 -0500 (EST), Bob Bruninga wrote:
>>The old Trimble SV6's (or something like that) did not have the RMC
>>sentences. But they are from 1995, and not very good, so I suspect
>>not to many are still around.
>
>Yes, But the last thing we want is for "APRS" software to be
>selectively ignoring many of our older trackers just for the
>programmers convenience. All of thse are supposed to be supported in
>"APRS" programs:
>
>GGA,RMC,GLL,VTG as a minimum and optionally GLB,RMZ and HDM
>
>In fact, NMEA 0183 shows these as required I think also...
>
>Bob
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Subject: Re: GPGGA with no GPRMC?
From: Bob Bruninga <bruninga@usna.edu>
Date: Fri, 19 Dec 2003 15:07:33 -0500 (EST)
X-Message-Number: 28
On Fri, 19 Dec 2003, Jeff King wrote:
>Maybe, but I suspect Scott is asking because of his OpenTrack tracker he
>is working on. There are only so many boatanchors you can drag along,
>and the fewer he drags along, IMHO, the better the protocol will be.
Good point, if he doesnt want his -tracker- to be compatible with older
GPS's that is his choice.
I guess I was speaking to the more general application of client software
which I would hope would support ALL APRS formats, not just selective ones
(that is the disintegration of APRS by partial implementations that alarms
me...). Anything that is going to decode APRS off the air in my opinion,
must receive all NMEA formats or it is leaving many existing operators off
the maps, and that is not good practice...
Again, you are right about the tracker... I'm just clarifying a bit what
I wrote. thanks...
Bob
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Subject: Re: GPGGA with no GPRMC?
From: Jeff King <jeff@aerodata.net>
Date: Fri, 19 Dec 2003 15:32:28 -0500
X-Message-Number: 29
On Fri, 19 Dec 2003 15:07:33 -0500 (EST), Bob Bruninga wrote:
>I guess I was speaking to the more general application of client
>software which I would hope would support ALL APRS formats, not just
>selective ones (that is the disintegration of APRS by partial
>implementations that alarms me...). Anything that is going to
>decode APRS off the air in my opinion, must receive all NMEA formats
>or it is leaving many existing operators off the maps, and that is
>not good practice...
Right, but he is not making a client nor should the NMEA spec define what
goes over the air, it is the actual AVL protocol that should do that, be it
APRS or OpenTrak.
So, while the APRS spec may call for clients to be able to decode NMEA over
the air, I hope you would agree with me that any new tracker author, chose
the most compact over the air protocol possible. Since it is in the spec,
then any client should be able to decode it, APRS or OpenTrak issues aside.
( correct me if I am wrong, but I think this would be the compressed format
for APRS and garmin binary for OpenTrak).
----------------------------------------------------------------------
Subject: Re: GPGGA with no GPRMC?
From: James Jefferson <jj@aprsworld.net>
Date: Fri, 19 Dec 2003 14:39:19 -0600
X-Message-Number: 30
Bob B wrote:
>Yes, But the last thing we want is for "APRS" software to be selectively
>ignoring many of our older trackers just for the programmers convenience.
>All of thse are supposed to be supported in "APRS" programs:
He's just talking about what sort of sentences his tracker needs to parse for
transmit. There's nothing wrong with him making his tracker only work with
modern GPSes - it does nothing but limit his customers.
-Jim
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