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ZL3AI > APRDIG 12.05.04 09:52l 239 Lines 9979 Bytes #999 (0) @ WW
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Subj: TAPR Digest, Apr 22, 2/10
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: kallen2@bellsouth.net
From: Gerry Creager N5JXS <gerry.creager@tamu.edu>
Date: Thu, 22 Apr 2004 09:17:36 -0500
X-Message-Number: 7
OK, folks. First seminar announcement. I'm working on a presentation
to this group on GPS accuracy and error budgets.
Short form: Observational results since Selective Availability was
turned off indicate the typical accuracy versus a known, surveyed point,
either informal or as recognized by the National Geodetic Survey, or the
International GPS Service for Geodynamics, using an L1, code-phase
receiver (consistent with the GPS receivers most on this Sig use) is on
the order of a 6-meter radius circle for 95% probability (roughly
2-sigma). Vertical accuracies vary. I don't do code-phase vertical
because the results are too ambiguous.
Centimeter accuracies can be achieved using multiple L1/L2 GPS
receivers, occupying the control points and point of interest
simultaneously, and subsequently post-processing the data to create
baselines and a geometric network of controlled position points (on
your known monuments) and the point of interest. The final coordinates
of the point of interest are determined as the lowest residual solution
of a least-squares adjustment of the entire network within the
constraints of the control points. 1 cm horizontal (2-sigma) error
circles can be achieved this way. 3 cm vertical (2-sigma) error spheres
are achievable using some only slightly modified procedures but the same
concepts.
In very general terms, using a well-configured DGPS system will enhance
accuracy by about an order of magnitude: a 6m error would resolve to a
little over a half meter. Differential doesn't work for the
dual-frequency, baeline-derived calculations. DGPS is for code-phase
corrections only.
Real-time kinematic surveying can achieve roughly 5-10cm accuracies by
linking the error parameters from a base station to the roving reciever
in real time. The easiest explanation for this is DGPS on steroids.
'Nuff said for now. I'll be back.
gerry n5jxs
--
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: From: "KC2MMi" display the position data?
From: "K. Mark Caviezel" <kmcaviezel@yahoo.com>
Date: Thu, 22 Apr 2004 07:36:10 -0700 (PDT)
X-Message-Number: 8
From: "KC2MMi" <kc2mmi@verizon.net>
Date: Wed, 21 Apr 2004 13:57:36 -0400
X-Message-Number: 13
Bob?
<Name me ONE thing that you think the Kenwood Mobile Radio APRS capability
is "holding back" for the mobile or hand-held user? And I bet I can think
of a way to do it with a little ingenuity instead of a lot bitching...>
One thing. Well, two things if you can do them both.
When the D7 is used with a headless GPS (i.e. hockey puck) can you make it
display the position data and EPE data from the GPS?
All I want is to see the same DDD.MM.mmm that my GPS is putting out, on the
radio.
>I haven't seen EPE data, but just hit the POS (3) button. The degrees
and minutes symbols with flash at 1 Hz as long as good NMEA is coming into
the D7. If the GPS powers down or loses lock, that flashing will stop.
73's de
KMC ac0ack Denver, CO
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Subject: Re:Website for APRS station info
From: Clair Dunn <cadunn@vt2000.com>
Date: Thu, 22 Apr 2004 11:10:05 -0400
X-Message-Number: 9
Aghh -- I commited a sin. One I particularly hate.
I meant to (at the end of my website suggestion yesterday) offer to do
it. I forgot. I'll make the site, very simple, and accept text docs from
anyone who will take the effort to write up the station setup they use
for APRS.
I have my own server and can do this.
Clair, W1CQD
Certified SKYWARN Spotter
Member ARRL, FISTS, 10-10
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Subject: Re:Website for APRS station info
From: "Curt, WE7U" <archer@eskimo.com>
Date: Thu, 22 Apr 2004 08:14:52 -0700 (PDT)
X-Message-Number: 10
On Thu, 22 Apr 2004, Clair Dunn wrote:
>Aghh -- I commited a sin. One I particularly hate.
>
>I meant to (at the end of my website suggestion yesterday) offer to do
>it. I forgot. I'll make the site, very simple, and accept text docs from
>anyone who will take the effort to write up the station setup they use
>for APRS.
>
>I have my own server and can do this.
If you install a Wiki instead, people can update the pages themselves, and
you can spend you efforts correcting typos and reorganizing the pages
instead. Much better use of your time.
You'd also have to post something periodically reminding people about it.
--
Curt, WE7U archer at eskimo dot 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!"
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Subject: Re: APRS greater precision
From: "KC2MMi" <kc2mmi@verizon.net>
Date: Thu, 22 Apr 2004 11:39:25 -0400
X-Message-Number: 11
<Sir, I don't know about others, but I am not a very financially forward
person. It's the antiquated equipment you speak of at very low prices
that has allowed me to experiment further into APRS by using DOS
programs. >
Keith, I refer to it as "The Shorts". As in, I reach for my wallet and all
I come up with is my shorts. It's a common enough problem these days. And,
our financial problems are simply not a relevant reason to hobble progress
in any field.
I'm not saying to make the equipment more expensive or the club more
exclusive. I'm saying to extend APRS to address those things it doesn't
address now. The alternative is that APRS, like your DOS computer, will stay
as it always has been. And the rest of the world will migrate to a newer
more capable platform--leaving you totally out of the picture with no hope
or chance of upgrading at all, ever.
Is that a better alternative than extending APRS so that an upgrade becomes
possible one day? OK, if you say so.
Look on the bright side: A radio like the THD7 is already obsolete, it DOES
NOT support the existing APRS capabilities. If Kenwood builds a THD8 to
support "APRS3" then the price of the obsolete THD7's will drop, as obsolete
equipment always does, and you'll be more likely able to afford better
equipment sooner. And, upgrade or migrate along the way, instead of throwing
out whatever you have.
There are win-win solutions and ways to extend a spec without crippling the
older equipment. But simply freezing the spec and forcing users to develop a
new one? That's a lose-lose situation for all APRS users. There's no point
in that, even if it looks good because it would be free.
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Subject: Re: Additional thoughts on the great debate....
From: "Curt, WE7U" <archer@eskimo.com>
Date: Thu, 22 Apr 2004 08:47:27 -0700 (PDT)
X-Message-Number: 12
On Wed, 21 Apr 2004, Jim Duncan wrote:
>Clearly we are witnessing major growing pains and with that growth we
>seem to be fast approaching a brick wall without our federally-mandated
>restraint and safety devices properly engaged.
I've seen most of the discussions as relatively _minor_ growing pains.
Perhaps the volume of e-mail between the interested parties makes people
think it as more major than it is? If it's important to people, they will
post on it.
For the most part, the spec works. There are just a few nagging issues
here and there. Two of them are being discussed concurrently on the
APRSSIG.
Ambiguity: I suspect that Bob and a group of us just can't come to
agreement on the ambiguity stuff, there's just too much of a disconnect on
that one. As it isn't extremely important to most people, I suspect it
will get dropped again. Perhaps there's a good reason that this one keeps
popping up every few years Bob?
Precision: I'm still hopeful that this thread will actually lead to
something. Bob has changed his mind with respect to promoting Base-91
Compressed posits (which are in the ratified spec), so that only leaves us
NMEA posits with more digits after the decimal point to support higher
precision, like the TinyTrak-3 and perhaps the OpenTracker can do.
I'd really like to see the Base-91 compressed posits supported exactly as
listed in the spec, for posits, objects, and items. It gives us the
resolution that we currently need for SAR, plus the rest of the APRS
features. NMEA posits aren't adequate, as we can't represent objects/items
with those.
Xastir fully supports Base-91 compressed posits, objects, and items,
exactly as specified in the APRS Spec. I can do useful things with those
during SAR missions, and cannot do those things at all without the
compressed mode. Perhaps it is an advantage after all, as I can create
compressed objects/items at will and post them on the map, and few others
can see them/manipulate them.
We could also talk about mixed-case object/item names. Jim (WA6OFT), does
UI-View support those now to the extent that they can take over Xastir's
objects that are mixed-case or lower-case? Jim and I ran experiments on
Firenet several times to investigate interoperability of UI-View32 and
Xastir. Modifications to both programs resulted from that, so it was a
good exercise.
--
Curt, WE7U archer at eskimo dot 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!"
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