i agree eglysd being unmarked would have been another good point to try this hit or miss
experiment upon
which i have just described in a crossing post for nyonqc
to see if it really would make a difference
but we would still have needed to know its legally defined datum first
which we dont
so we cant say for sure the way i hope to be able to do for nyonqc
certainly not doable on azconmut tho
or any other such visibly marked point
--- In BoundaryPoint@yahoogroups.com, "Hugh Wallis" <hugh@o...> wrote:
>
> If you recall the start of this thread (which has change titles a few times
> now) it was the Lat and Long information provided for the US state
> quadripoint which kicked it all off - that was the initial connection to
> multipointing.
>
> I believe it also has relevance to the EGLYSD class B claim discussed in
> another thread - the location evidently reached was the confluence according
> to WGS84 datum which is most likely not the same location as the actual
> tripoint which was probably defined using a different datum. Some of these
> datums can cause points to be off by up to 200m in some parts of the world
> so datum awareness is vital if you are going to use Lat and Long as the
> means of identifying multipoint locations.
>
>
> _____
>
> From: BoundaryPoint@yahoogroups.com [mailto:BoundaryPoint@yahoogroups.com]
> On Behalf Of aletheiak
> Sent: Tuesday, January 03, 2006 9:20 PM
> To: BoundaryPoint@yahoogroups.com
> Subject: [BoundaryPoint] Re: ok but why or what are we looking for
>
>
> ok thanx i get it
> but i am also still trying to figure out if there is anything useful for
> trypointing in these
> conversations that is somehow still eluding me
>
>
> for reasons mostly just explained
> the choice of datum has rarely if ever made a difference in our
> multipointing tries
>
> i dont say it absolutely couldnt make a difference but it evidently hasnt
> yet
>
> &
>
> such variations or deviations in data as you guys are reporting here come as
> no surprise
> i trust
> yet their exact cause or causes are at the same time unknown & unknowable
> because
> the variables are too great as well as too numerous to permit any
> conclusions about any
> single bit of data
> let alone any generalizations about the whole of it
> except that
> trypointing by gps might become very slightly more or less tentative
> approximative fudgy
> & sketchy than it already is depending on which datum you choose
>
> so on both counts
> these observations seem to me to be not useable information but rather the
> absence of it
> for our purposes here
> or at best a partial description of what is for us only a hypothetical data
> gap anyway
>
> the data that are most useful to us here in trypointing are those which
> narrow & focus the
> search & the perception rather than diffuse them
>
> as soon as someone actually applies any of this info to a real try
> & it makes a difference in the outcome
> i would of course immediately change my appraisal of it
>
> --- In BoundaryPoint@yahoogroups.com, "Hugh Wallis" <hugh@o...> wrote:
> >
> > Each entry made records the actual WGS84 coordinates displayed on a GPSr
> > device that is positioned at a physical marker which is marking the Prime
> > Meridian. The point is to demonstrate, pursuant to the preceding
> > conversation here, that the choice of datum when reporting Lat and Long is
> > relevant. Frequently the WGS84 reading will show other than 0° 0.000" E/W
> > because different datums (data ?) than WGS84 have been used when placing
> the
> > physical markers. This is not a scientific survey of course, nor can it be
> > used in any way to deduce errors elsewhere. It is simply for illustration
> > and one of the larger collections of such "in the field" reports of such
> > deviations that I am aware of. It adds additional information to what
> Roger
> > found from Google Earth.
> >
> >
> > _____
> >
> > From: BoundaryPoint@yahoogroups.com [mailto:BoundaryPoint@yahoogroups.com]
> > On Behalf Of aletheiak
> > Sent: Tuesday, January 03, 2006 4:46 PM
> > To: BoundaryPoint@yahoogroups.com
> > Subject: [BoundaryPoint] ok but why or what are we looking for
> >
> >
> > --- In BoundaryPoint@yahoogroups.com, "Hugh Wallis" <hugh@o...> wrote:
> > >
> > > Take a look here where the difference between WGS84 and various other
> > > "observations" is documented at various locations along the prime
> meridian
> > >
> > > http://tinyurl.com/76jv4
> > >
> > >
> > > _____
> > >
> > > From: BoundaryPoint@yahoogroups.com
> [mailto:BoundaryPoint@yahoogroups.com]
> > > On Behalf Of Roger McCutcheon
> > > Sent: Tuesday, January 03, 2006 6:20 AM
> > > To: BoundaryPoint@yahoogroups.com
> > > Subject: Re: [BoundaryPoint] Four pointer
> > >
> > >
> > > I went to maximum magnification on Google Earth and found that it did
> > indeed
> > > show zero longitude as being about three quarters of the way to the far
> > side
> > > of Black Heath Avenue, to the east of the Zero Meridian in the Royal
> > > Observatory, so then I went to the Prime Meridian site and found that
> "the
> > > zero meridian on the WSG84 datum, which is about 100 metres to the east
> of
> > > the line marked at Greenwich, is an average of the various continental
> > > movements", so we need not worry: someone is paying attention! Roger
> > > McCutcheon.
>
>
>
>
>
>
> _____
>
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