Chris Olsson wrote:
>Leaving aside the semantic issue of whether the differences between national
>datums constitutes an "error", I think it is worth noting that such differences
>tend to be more than 50 metres rather than less. WGS84 itself is more than a
>hundred metres of Longitude from the Prime Meridian at Greenwich and many
>national datums are also more than 50 metres either from the old Prime Meridian
>system or from WGS84.
Irrelevant to visual satellite observing.
>As for the error range of the TLEs being 500 metres, I'm surprised if it is
>true that precise elsets are no better than half a kilometer.
I did not say that. You have distorted my words. I said that I was
happy if I could derive an elset for a classified object based on visual
observations that was accurate to 500 meters. Since you have never tried
to do anything like that, it would seem that my sentence didn't make any
sense to you.
>Perhaps Dr TS
>Kelso and others are wasting their time when they produce excellent
>computational software which outputs to an arc-second of declination and to a
>metre of orbital height?
They wasted their time "once" - when they created their programs.
They are wasting our time many times - if we are dumb enough to actually
print out such predictions.
>Will you tell, them?
Why bother? They don't really care. Most of them do not make visual
satellite observations. None of them make "positional observations".
None of them use positional observations to derive element sets for
classified objects. They do not have any experience in this field.
And someone who advocates 5 decimal places in lat/long positions
obviously has no experience in this field either.
>Are you suggesting that SpaceCom somehow deliberately degrades the orbital
Your "straw men" arguments are silly and way, way "off topic".
This SeeSat-L mailing list is for visual satellite observations.
Your posts on "geodetic precision" are no longer interesting and
are "off topic".
>There are even greater differences elsewhere in the world, if you care to look
>for them. That is why it is important to state the geodetic basis of
>apparently precise co-ordinates.
When you have actual observers in those parts of the world and they
submit accurate observations that appear to have unexplained systematic
residuals greater than 500 meters, then I will be interested. I do
not hope to live that long considering how your posts have raised
my blood pressure the last few days.
>You could, I suppose, replace the ellipse of rotation with a simple sphere, but
Your "straw man" arguments are really, really silly.
>All I have suggested is that we should have some common Lingua Franca when
>expressing that position.
I am expressing my opinion that you have no experience in what a very
few of us are doing. My opinion is that your suggestion is completely
superfluous.
>Yes, there are those who will exhort us to dumb down our co-ords to two places
Your "straw man" arguments are really, really silly.
>I suggest that those who care about precision; and those who understand the
>difference between accuracy and precision: give a thought to what those
>concepts actually mean and present suitable labels upon their stated co-ords.
I suggest that they not concern themselves with the subject.
>Since I have broached the subject on the List. I have noticed that several
>List-members have admirably done so
I have convinced one that it was silly and he has now removed "WGS84" from
his signature.
>and I have also received a remarkable
>number of non-hostile private communications from others who are also
>interested in making good use of the data which they have at their disposal.
I am not one of those and I request that anyone sending you a non-hostile
communication send me a copy so I can explain to them how the real world
really works.
>I think it was Albert Einstein who once said that:
>
>The Truth ought to be expressed as simply as possible, but never more so.
Sophocles: "The truth is always the strongest argument".
We have been making obs and generating elsets. You showed up a week
ago for the first time.
Eistein: "As far as the laws of mathematics refer to reality,
they are not certain, and as far as they
are certain, they do not refer to reality."
SGP4 may be mathematically precise, but the reality of human visual
satellite observation means 5 significant figures is quite enough.
Mike McCants
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This archive was generated by hypermail 2b29 : Tue Aug 21 2001 - 09:16:16 PDT