Subject: Re: but why suppose an eglysd datum has ever been stated or even can be synthesized
Date: Jan 11, 2006 @ 19:11
Author: aletheiak ("aletheiak" <aletheiak@...>)
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--- In BoundaryPoint@yahoogroups.com, "Hugh Wallis" <hugh@o...> wrote:
>
> Not necessarily - different datums do not give rise to absolutely parallel
> lines of longitude and lattitude when compared with each other. They are
> generally slightly mutually skewed unless they are based on the same
> ellipsoid.
>
>
> _____
>
> From: BoundaryPoint@yahoogroups.com [mailto:BoundaryPoint@yahoogroups.com]
> On Behalf Of aletheiak
> Sent: Wednesday, January 11, 2006 1:45 PM
> To: BoundaryPoint@yahoogroups.com
> Subject: [BoundaryPoint] Re: but why suppose an eglysd datum has ever been
> stated or even can be synthesized
>
>
> & actually this whole excursion into datum shifts will prove unnecessary if
> we can get our
> southernmost egly rock coords in wgs84
> in which case the latitudinal eglysd displacement in wgs84 would of course
> be zero
> & only the longitudinal displacement from the 25th meridian would have to be
> replicated
> from the southernmost rock down to eglysd
>
> of course
>
> which was my initial impression & proposed method
>
> & i really neednt complicate or compromise it with any questions arising
> from datum shift
> especially if they never arise
>
> --- In BoundaryPoint@yahoogroups.com, "aletheiak" <aletheiak@y...> wrote:
> >
> > thank you
> > thank hugh
> > huge thanxx & hugs
> >
> > & a few intertwingles follow
> >
> > --- In BoundaryPoint@yahoogroups.com, "Hugh Wallis" <hugh@o...> wrote:
> > >
> > > >>because the far greater component of any datum shift
> > > displacement
> > > both potentially & typically i believe
> > > is in the longitude rather than the latitude
> > > <<
> > >
> > > At http://www.colorado.edu/geography/gcraft/notes/datum/edlist.html
> (a.k.a.
> > > http://tinyurl.com/8sexy - a fortunate coincidence - easy to remember at
> any
> > > rate - hope it makes it through eveyone's spam filter) you can see the
> datum
> > > shift from Local to WGS84 for many datums for long and lat in the dx and
> dy
> > > columns (in metres). While the above assertion is true in some cases, if
> we
> > > look at the datums that have typically been used for Egypt (European
> 1950
> > > giving dx = -130 and dy = -117, Old Egyptian 1907 giving dx = -130 and
> dy =
> > > 110), the lat and long displacements are not really "far greater"
> although
> > > they are greater. If we look at those typically used for Sudan (Adindan
> > > gving either dx = -166 and dy = -15 or dx = -161 and dy = -14) then they
> > > are, however. Libya does not appear in the table.
> > >
> > > In some parts of the word the shift difference is the other way around -
> > > e.g. Indonesia and much of South East Asia, some users of the European
> 1950
> > > datum such as Spain and Portugal, and various remote islands, almost all
> > > users of NAD27 i.e., Canada, USA, Central America, much of Eastern
> Europe
> > > using S-42.
> > >
> > > It seems as though a general statement cannot be made therefore and that
> > > every datum comparison needs to be done independently.
> >
> > you are right
> > a general statement cant be made if you drag the exceedingly anomalous &
> inapplicable
> > east indies into this african desert once again
> >
> > & at the same time you are right on again in having very much corrobrated
> for us the
> full
> > extent of practically all the anomalies or variables that are actually
> applicable here
> > for which i am exceedingly grateful
> > & which does amply sustain my general statement & approach in this
> particular case
> >
> > so i should add to your excerpted swatch above
> > & thanx to your attention
> > if not far far greater
> > as seems far likeliest
> > then still unquestionably greater in any case
> >
> > & therefore
> > we can now fully expect eglysd to be noticeably closer
> > to the 22nd parallel than the eglys rock is to the 25th meridian
> > in any known local datum including most particularly wgs84
> >
> > even if not absolutely necessarily much closer
> > or very much closer
> >
> >
> > & thats the point here
> > specifically
> > to get as close as possible to eglysd with what we actually do have to go
> by
> > & where anything indonesian etc is almost definitely again a pure mirage
> >
> > unless you were trying to make a different point that i missed
> >
> > & one more insert below
> >
> > > On Brownlie - if anyone has access to a copy, some relevant references
> are
> > > found at http://arabworld.nitle.org/texts.php?module_id=3
> > > <http://arabworld.nitle.org/texts.php?module_id=3
> <http://arabworld.nitle.org/texts.php?module_id=3&reading_id=119&sequence=6>
> &reading_id=119&sequence=6>
> > > &reading_id=119&sequence=6 (a.k.a. http://tinyurl.com/b89pu ) summarised
> > > therin thus: "Libya's eastern borders result from agreements between
> Egypt
> > > and Italy in 1925 and 1926, which superceded (sic) an earlier
> arrangement
> > > between the Ottoman empire and Egypt in 1841, and from agreements in
> 1934
> > > between Britain and Egypt (as the condiminium powers in Sudan) on the
> one
> > > hand and Italy on the other. The latter agreement transferred the Sarra
> > > triangle to Libya - the territory allocated to Sudan under the 1899
> > > convention and lying to the south of the 22N parallel (Brownlie 1979;
> > > 102-109, 133-140).". This secondary (or is it tertiary) source is quite
> > > likely accurate, but, of course, may not be complete (which is what you
> are
> > > hoping I guess).
> >
> > thank you
> > this is again very much to the point
> > & tho nothing new beyond what we have seen in ibs 10 & 18 & 61
> > the fact that you promise 15 more pages gives reason to pursue this anyway
> > along with the fact that it is a good decade or 2 more recent than the ibs
> studies
> >
> > end inserts
> >
> > >
> > >
> > > _____
> > >
> > > From: BoundaryPoint@yahoogroups.com
> [mailto:BoundaryPoint@yahoogroups.com]
> > > On Behalf Of aletheia kallos
> > > Sent: Wednesday, January 11, 2006 11:06 AM
> > > To: boundaryPoint@yahoogroups.com
> > > Subject: Re: [BoundaryPoint] Re: but why suppose an eglysd datum has
> ever
> > > been stated or even can be synthesized
> > >
> > >
> > > thanxx
> > > i appreciate the question no less than the critical
> > > review behind it
> > > but first
> > > with regard to the egsd signs
> > > all indications thus far are that they date from the
> > > militarily tense early to mid 1990s period
> > > so their accuracy was very likely limited by selective
> > > availability in any case
> > >
> > > & regarding egly
> > > yes indeed i could & probably should ask this just to
> > > rule it out with greater certainty
> > > tho i have already given my reasons for doubting there
> > > is a bilaterally official datum even there
> > > in my previous post
> > > to which i should now add that the elusiveness or
> > > formlessness of all those so hopefully lovely egly
> > > border arcs
> > > which arent at all discernible as arcs on any maps i
> > > have yet seen
> > > is just one more indication of the crudeness & hence
> > > datumlessness of the 1927 egly demarcation survey
> > >
> > > & yikes reason even to doubt that the commissioners
> > > would have been proud enough of their handiwork in the
> > > wilderness to even plat it out
> > > or worry about it in any other way much beyond
> > > degmindec or degmindodec
> > > let alone degminsec etc
> > >
> > >
> > > but in the meantime i also realized that tho my
> > > proposed 487 mile extrapolation from the nearest egly
> > > rock would nail the longitude of eglysd with as much
> > > precision as that rock itself had already been nailed
> > > with
> > > it still wouldnt at all necessarily nail the latitude
> > > of eglysd any better than we already have it
> > >
> > > 22nd parallel
> > >
> > > hahahahaha
> > >
> > > ahhh
> > >
> > >
> > > nevertheless i believe this will prove to be a smaller
> > > shortcoming than one might initially think
> > > because the far greater component of any datum shift
> > > displacement
> > > both potentially & typically i believe
> > > is in the longitude rather than the latitude
> > > since latitude is first a sidereal fact while
> > > longitude is only a terrestrial & far more subjective
> > > one
> > >
> > > meaning all possible versions of the 22nd or any other
> > > parallel will bunch up much closer together generally
> > > than will all possible versions of the 25th or any
> > > other meridian
> > >
> > >
> > > for example the example i think we may have begun with
> > >
> > > azconmut shifting between nad27 & nad83
> > > has 59 meter longitudinal displacement & only 2 meter
> > > latitudinal
> > > which btw per pythagoras means more than 99point94
> > > percent of the distance of any shift there is
> > > contributed by the longitudal portion of the shift
> > > alone
> > >
> > > so our range of possible latitude values here at
> > > eglysd should be a correspondingly small fraction of
> > > the distance from the 25th meridian of the
> > > southernmost egly rock
> > > in whatever datum it is bagged & or expressed
> > >
> > > which means
> > > using say pilotage gps on the southernmost egly rock
> > > we would get the correct submeter wide ribbon of
> > > longitude for eglysd in any datum
> > > & but only the correct say meter or at most several
> > > meter broad ribbon of latitude for it
> > >
> > > & thus using commercial gps any datum shift in the
> > > latitude would most likely be imperceptible
> > >
> > >
> > > & tho i thought of this saving grace shortly before
> > > falling asleep last night
> > > the confirmation of it came to me in a dream
> > > from which i awoke laughing out loud
> > >
> > > in the dream i had just reached eglysd by car & found
> > > a border guard there with his young son who was
> > > operating a walkie talkie
> > >
> > > of course the guard asked me to open my trunk
> > > which i did
> > > & inside it
> > > much to my surprise
> > > was his other son
> > > an identical twin for all i could tell
> > > talking back to them on another walkie talkie
> > >
> > > hahahahaha
> > >
> > > & smiling & shaking my head in amazement ever since
> > >
> > > can you dig it
> > >
> > >
> > > but anyway
> > > where do i think we are now
> > >
> > > i think
> > > we are beginning to think mohamed wont answer perhaps
> > > because he doesnt know
> > > & we are looking for brownlie just to check as much as
> > > we can of our guesswork to date
> > > as well as to get a better fix on any potential source
> > > docs
> > >
> > > but actually
> > > it just occurs to me too
> > > since this southernmost egly rock
> > > which we are trying to hang our hat on
> > > is so beguilingly close to the 29x25 project
> > > intersection point
> > > why dont we just sponsor a fellowship for some
> > > deserving confluencer to bag it for us
> > >
> > > --- "Lowell G. McManus" <lgm@w...> wrote:
> > >
> > > > While you're corresponding with them, couldn't you
> > > > just ask if there is an
> > > > official datum for the delimited but undemarcated
> > > > portions of the EGLY boundary
> > > > and what datum they used when erecting the
> > > > (presumably) unilateral signs on
> > > > EGSD? Wouldn't that beat trying to extrapolate from
> > > > afar?
> > > >
> > > > Lowell G. McManus
> > > > Leesville, Louisiana, USA
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "aletheiak" <aletheiak@y...>
> > > > To: <BoundaryPoint@yahoogroups.com>
> > > > Sent: Tuesday, January 10, 2006 9:36 PM
> > > > Subject: [BoundaryPoint] Re: but why suppose an
> > > > eglysd datum has ever been
> > > > stated or even can be synthesized
> > > >
> > > >
> > > > > aha & far better
> > > > > we just ask the egypt border force if it happens
> > > > to have gps era survey data
> > > > > on this
> > > > > southernmost egly marker at any level of
> > > > exactitude
> > > > > & extrapolate eglysd from it
> > > > > aha
> > > > > of course
> >
>
>
>
>
>
>
>
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