Boiling it down to actual numbers:
Points defined using the datums typically used in Egypt are
approximately 130m meridianally distant and 117m lattitudinally
distant (resulting in a total straight line distance of sqrt(130^2 +
117^2) = 175m approx) from a point that has the same coordinates expressed as
WGS84.
Points defined using datums typically used in the
Sudan are approximately 166m meridianally distant and
14m lattitudinally distant (resulting in a total straight line
distance of sqrt(166^2 + 14^2) = 166m approx) from a point that has
the same coordinates expressed as WGS84.
So if an Egypt based datum was used then it is not clear to
me that the lattitudinal difference would be "far" less than the meridianal
difference (~117m vs ~130m)
>>a
general statement cant be made if you drag the exceedingly anomalous &
inapplicable
east indies into this african desert once
again<<
well sure - not just east indies but
also USA and Canada (1927) and Eastern Europe - its all in the numbers
really and that's just where they happen to differ differently :) - and that's
the point I was trying to make really - just that it's "all in the numbers"
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&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