From: Ralph Hartley (hartley_at_aic.nrl.navy.mil)
Date: Mon Feb 12 2001 - 16:08:25 CET
Received: (from mdom_at_localhost) by karto.ethz.ch (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) id QAA08324 for cavexml-outgoing; Mon, 12 Feb 2001 16:05:13 +0100 Received: from sun0.aic.nrl.navy.mil (sun0.aic.nrl.navy.mil [132.250.84.10]) by karto.ethz.ch (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) with ESMTP id QAA08319 for <cavexml_at_cartography.ch>; Mon, 12 Feb 2001 16:05:12 +0100 Received: from aic.nrl.navy.mil (pc31.aic.nrl.navy.mil [132.250.84.181]) by sun0.aic.nrl.navy.mil (8.9.3+Sun/8.9.3) with ESMTP id KAA05244 for <cavexml_at_cartography.ch>; Mon, 12 Feb 2001 10:05:14 -0500 (EST) Message-ID: <3A87FC69.4080606@aic.nrl.navy.mil> Date: Mon, 12 Feb 2001 10:08:25 -0500 From: Ralph Hartley <hartley_at_aic.nrl.navy.mil> User-Agent: Mozilla/5.0 (X11; U; Linux 2.2.16-22 i686; en-US; m18) Gecko/20010124 X-Accept-Language: en To: cavexml_at_cartography.ch Subject: Re: Other areas that haven't been discussed. References: <Pine.GSO.4.05.10102091135400.11013-100000_at_cor.oz.cc.utah.edu> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-cavexml_at_karto.baug.ethz.ch Precedence: bulk Reply-To: cavexml_at_cartography.ch
John Halleck wrote:
> On Fri, 9 Feb 2001, Ralph Hartley wrote:
>
>>>
>>> Identification of some set of loops.
>>> I assume that reasons for this would be obvious.
>>
>> I would classify this as a special case of "Intermediate" processing
>> information. For some ways of processing the data(sequential loop
>> closure, the number of possible loops can be astronomical) this sort of
>
> Astronomical? For minimal loops it can't be any worse than the
> redundancy. I'm not talking ALL (redundant), just a minimal set.
> (For a survey with 1000 points and 1100 shots, there can only
> be 100 loops in a minimal set. (Which can be derived from the
> spanning tree + the shots not in it.)
I mean there are an astronomical number of loops to choose from to form
a minimal set, not that any particular minimal set will have an
unreasonable number of loops. Is it allways the case that any minimal
set of loops is uniquely determined by a spanning tree?
Also, talk of *a* spanning tree seems to imply that all the stations are
connected. Unfortunately, hanging surveys are rather common, and need to
be handled.
> But even in "pure" least squares, it will be needed to try to identify
> the blunders if the reference variance of the adjustment is too high.
I know I am being a little pedantic here, but identifying blunders is
not a part of least squares at all.
>
>> The
>> minimal spanning tree is fairly easy to recompute, but an unclosed line
>> plot depends on a particular tree, that may not be minimal in any sense
>
>
> But the unclosed line plot can be read off of a minimal spanning tree.
Off the spanning tree used to make the plot. That might not be a minimal
spanning tree.
>
>> (often it is determined by historical accident). Any description of the
>> unclosed lineplot must (explicitly or not) describe that tree.
>
>
> I was campaining for an explicit tree, because it has more uses
> than just the line plot.
I agree. An unclosed line plot has two parts: a tree, and the
coordinates of the points. The tree needs to include the closing shots
to the "unclosed images" of tie in stations. It is relatively easy to
recompute the lineplot given the original data and the spanning tree
used. Given a lineplot it is easy to get the spanning tree it was based on.
A good format for a lineplot should make the spanning tree easy or
trivial to obtain (e.g. it could contain an explicit tree).
Ralph Hartley
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