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ZL3AI > APRDIG 14.05.04 22:40l 240 Lines 9590 Bytes #999 (0) @ WW
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To : APRDIG@WW
TAPR APRS Special Interest Group Digest for Monday, April 26, 2004.
1. Re: Compromise proposal (was: Re: The APRS-WG and spec improvements.)
2. Re: Compromise proposal (was: Re: The APRS-WG and spec improvements
3. Re: Compromise proposal
4. Re: Compromise proposal (was: Re: The APRS-WG and spec improvements
5. Re: Compromise proposal
6. Re: APRS+SA Programming
7. Re: Objects and D7 are easy.
8. Timeslotting
9. Re: Objects and D7 are easy.
10. Re: Timeslotting
11. neat GPS, but not for the faint of heart
12. Re: Timeslotting
13. Re: Timeslotting
14. Re: Objects and D7 are easy.
15. Re: Objects and D7 are easy.
16. Re: Objects and D7 are easy.
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Subject: Re: Compromise proposal (was: Re: The APRS-WG and spec improvements.)
From: "Jordi Costa" <bvjordi@bitsnvolts.com>
Date: Mon, 26 Apr 2004 08:54:09 +0200
X-Message-Number: 1
Henk,
It is not a British problem. Spain uses EUR50 and migration to WGS84 does
not seem clearly scheduled. The same could be applicable to many European
countries.
Laurie,
Some Magellan GPSs allow local datum display while outputting WGS84 NMEA
data. Mine (Sportrak) does.
Jordi - EA3CIU
----- Original Message -----
From: "Laurie - g6isy" <g6isy@dsl.pipex.com>
To: "TAPR APRS Special Interest Group" <aprssig@lists.tapr.org>
Sent: Saturday, April 24, 2004 9:45 PM
Subject: [aprssig] Re: Compromise proposal (was: Re: The APRS-WG and spec
improvements.)
>Henk de Groot wrote:
>>Hello Laurie,
>>
>>>Our mapping agency does not plan to issue maps to WGS84.
>>
>>That doesn't surprise me, the Brits have a long histroy when it comes
>>to dealing with international standards...
>>
>
>Its not a matter of not wanting to use an international standard.
>In fact, as I said, our datum is defined as a transform from WGS84.
>Its a practical matter of our bit of the world not being a very good fit to
the
>WGS84 geoid and continental drift.
>The European land mass is moving relative to WGS84 at a considerable rate.
>If we were to issue precision maps using WGS84 then they would be wrong
almost
>as soon as they were issued. Correcting for the drift problem is part of the
>reason for maintaining a different datum.
>
>>>I hope this shows our problem more clearly.
>>
>>I understood this already, I hope you understand the compromise which
>>gives both sides what they want without a sacrifice to compatibility,
>
>I understand what you are trying to do. I just wish some of the GPS
manufactures
>did.
>If we could select a different display datum to the NEMA data we wouldn't be
>having this discussion :-)
>
>Anyway, I think I have made all the points that I wanted to, so I'll shut up
>now.
>
>73 Laurie - G6ISY
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Subject: Re: Compromise proposal (was: Re: The APRS-WG and spec improvements
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Mon, 26 Apr 2004 08:16:27 -0400
X-Message-Number: 2
Thats exacty what the proposed !DAO! format is all about. The "D"
character specifies the Datum, the "A" and "O" the added precision to 1
foot in Latitude and longitude.. And it can be applied optionally to any
position, object, or anything else. Bob
>>>Wes Johnston <wes@johnston.net> 4/25/04 8:31:32 PM >>>
I think what we need is instead of using 5 bytes to spell out WGS84 or
NAD27, we need to list all of them in a table and number them. One byte
gives us 256 datums. Surely there aren't that many... but hey, if there
are, add another byte for 65536 datums.
Wes
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Subject: Re: Compromise proposal
From: Gerry Creager N5JXS <gerry.creager@tamu.edu>
Date: Mon, 26 Apr 2004 07:44:15 -0500
X-Message-Number: 3
Jordi,
This is interesting... Magellan was hardly an early adopter of the GPS
Interface Control Document in its intent. I'm glad to learn the
Sportrak performs in that manner.
The original ICD-GPS-200 claimed the receiver would output the
WGS84-valid data via electronic means, while remaining silent on display
options. Most early receivers did not have a display of the data
directly.
The widespread adoption of GPS technology worldwide has raised this
issue more and more. The implementation of a variety of datums from
which to choose, and the parallel question of how to use a GPS with
current local datum implementations has been a long, and interesting
international debate. When it was solely a tool of the US military and
its allies, the issue was of little consequence, as the US Defense
Mapping Agency (now, the National Geospatial Intelligence Agency) made
the maps, or corrected the international ones of its allies, for use
with GPS. Then, as US civilian adoption became widespread, the US
Geological Survey, who are the originators of most of the cartographic
projects in my country, found themselves with a number of requests for
compatible maps and was unable to comply: Most of their maps were in
the NAD27 datum, and the transformation from NAD27 to WGS84 is not
straightforward across the continental extent of the United States. The
conversion process continues, although a large percentage of their map
holdings on paper (raster) have had NAD83 (which is close enough to
WGS84 for what we're talking about) coordinates added, and new products
are produced in NAD83.
With the international acceptance of GPS by consumers, the problems have
increased. NGIA is not responsible for converting all the maps of all
the countries, nor is USGS. However, the mathematical tools necessary
are available freely. The various cartographic agencies are on their
own to accomplish the task, and as you note, it is not a trivial problem.
The use of local datums for cartography and geodesy is founded in
simplifying the practices for a local area where the people doing the
work are not expecting a widespread redistribution of the maps or data,
or where the problems associated with working with broad, objective
systems are too great for the purpose at hand. In other words, when the
EURO50 datum was conceived, in 1950, the availability of high speed
computers was greatly limited, and the calculations were performed
manually, or with mechanical calculators. Thus, the ultimate precision
and the speed with which each calculation could be performed were
restricted. A truly worldwide datum was inconceivable and use of local
and regional datums was the norm, with good reason.
I anticipate that, with the rise of the Galileo GNSS, a new European
datum will arise, and a massive international effort to transform to
that will occur. Whether it is similar to WGS84... or even related...
remains to be seen, as the European partners have preferred in
discussions with US GPS experts, to ignore most of our lessons-learns;
this is unfortunate, as we've made a number of mistakes and learned from
most. I hope this is resolved before the first spacecraft is launched.
Even for ham radio and our tracking, this is really an international
problem and the various entities must work together to resolve it.
WGS84 is routinely adjusted as more information is available to make it
better fit the real world. It is also a dynamic datum where each point
should have a motion associated with it. That point is usually ignored
for our purposes, but was recognized by the datum designers.
Now, if we want a truly international datum and reference system, the
ITRF datum, updated annually, is likely the least controversial system.
WGS84 adjustments have brought that datum, over time, closer to the
current ITRF datum. The ITRF datum is maintained by the Central Bureau
of the International Earth Rotation Service.
Regards,
Gerry
Jordi Costa wrote:
>Henk,
>
>It is not a British problem. Spain uses EUR50 and migration to WGS84 does
>not seem clearly scheduled. The same could be applicable to many European
>countries.
>
>Laurie,
>
>Some Magellan GPSs allow local datum display while outputting WGS84 NMEA
>data. Mine (Sportrak) does.
>
>Jordi - EA3CIU
--
Gerry Creager -- gerry.creager@tamu.edu
Network Engineering -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Page: 979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843
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Subject: Re: Compromise proposal (was: Re: The APRS-WG and spec improvements
From: wes@johnston.net
Date: Mon, 26 Apr 2004 09:28:47 -0400 (EDT)
X-Message-Number: 4
This is what was referred to as !XYZ! last week, right? Now calling it
!DAO! ..... ok names aside, X or D is one character, right? That gives us
space to name (support) 26 datums at first glance. Eventually, we can
extend that to 90 characters (can't use the ! since it is a delimiter) for
identification of 90 datums. Gerry says he can think of 248 datums, so the
question at this point is do we want to just include the most popular
datums or support all the uncommon ones too?
Wes
On Mon, 26 Apr 2004 08:16:27 -0400, "Robert Bruninga" wrote:
>Thats exacty what the proposed !DAO! format is all
>about. The "D" character specifies the Datum, the
>"A" and "O" the added precision to 1 foot
>in Latitude and longitude.. And it can be applied
>optionally to any position, object, or anything else. Bob
ham callsign: kd4rdb
find me: http://wesvan.zapto.org
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