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#41
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Gene, we aren't doing ballistics here; we only want
to get close enough for the eyeballs to do the proper adjustments. For badge flights we try to exceed the minimums enough to make up for instrument errors; for record flights we must exceed the current record by a percentage that should account for these relatively minor distances. It's nice that someone is turned on by all this precision; in my mind it has all the usefulness of train spotting with respect to practicality in soaring. At 15:12 28 August 2003, Gene Nygaard wrote: Maybe Eratosthenes still thought the Earth was a near-perfect sphere, when he made a fairly reasonable calculation of its diameter Maybe Columbus wasn't even aware of the true shape of the poles. But we've known about the flattening at the poles for about four centuries at least, probably longer than nautical miles have existed. Certainly since long before the French scientists in the 1790s designed the meter to be 1/10000000 of the distance from the equator to the North Pole. We do, of course, have 360 degrees around the equator. When we agree on a starting point (e.g., the point where it crosses the meridian through Greenwich, England, the one most often used now), any particular place will always be the same number of degrees from it. We also have 90 degrees between the equator and either pole. The equator is always 0 degrees and the poles 90 degrees. But in between, there are at least three different ways of measuring latitude: geocentric latitude (the angle formed at the center of the Earth), geodetic latitude (the one normally used, the angle formed between the line normal to the tangent of the ellipsoid and the axis of rotation), and the angles used in the parametric formulas representing an ellipse. These don't agree with each other at any place not on the equator or the poles. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
#42
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In my line of work we speak of "measuring it with a micrometer, marking it
with a crayon, and then cutting it off with an axe". Bob Korves "Nyal Williams" wrote in message ... Gene, we aren't doing ballistics here; we only want to get close enough for the eyeballs to do the proper adjustments. For badge flights we try to exceed the minimums enough to make up for instrument errors; for record flights we must exceed the current record by a percentage that should account for these relatively minor distances. It's nice that someone is turned on by all this precision; in my mind it has all the usefulness of train spotting with respect to practicality in soaring. At 15:12 28 August 2003, Gene Nygaard wrote: Maybe Eratosthenes still thought the Earth was a near-perfect sphere, when he made a fairly reasonable calculation of its diameter Maybe Columbus wasn't even aware of the true shape of the poles. But we've known about the flattening at the poles for about four centuries at least, probably longer than nautical miles have existed. Certainly since long before the French scientists in the 1790s designed the meter to be 1/10000000 of the distance from the equator to the North Pole. We do, of course, have 360 degrees around the equator. When we agree on a starting point (e.g., the point where it crosses the meridian through Greenwich, England, the one most often used now), any particular place will always be the same number of degrees from it. We also have 90 degrees between the equator and either pole. The equator is always 0 degrees and the poles 90 degrees. But in between, there are at least three different ways of measuring latitude: geocentric latitude (the angle formed at the center of the Earth), geodetic latitude (the one normally used, the angle formed between the line normal to the tangent of the ellipsoid and the axis of rotation), and the angles used in the parametric formulas representing an ellipse. These don't agree with each other at any place not on the equator or the poles. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
#43
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#44
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Add one more, Bob.
Measure with a micrometer, Mark with a crayon, Cut on the safe side, with an axe, Grind to fit! JJ Sinclair |
#45
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#47
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Gene Nygaard wrote in message . ..
Yours is wrong in the 5th digit, and all the following ones are garbage. Once you go past the fourth digit, everything else in astronomy is speculation. Ask me if I give a ****. |
#48
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"George William Peter Reinhart" wrote in message ...
Troll = Ugly devil liviin' under a bridge, (see also motorcycle cops with radar guns (usually under a bridge)). Trolls = More than one ugly devil (also found in newsgroups) Trolling = Fishin' with fake bait from a slow boat. Cheers! As used on the Internet (source = Whatis?com): 2) As a verb, the practice of trying to lure other Internet users into sending responses to carefully-designed statements or similar "bait." I suspect that unless one's dictionary is very recent that the words "hacker" and "spam" would also not be defined as they are now used on the Internet, if they are defined at all. -Doug Hoffman |
#49
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Gene wrotethe
line normal to the tangent of the ellipsoid and the axis of rotation), and the angles used in the parametric formulas representing an ellipse. I got a little lost in all that, Gene, but I figure it all amounts to about half a mile (statute) in a 1000K flight. Anyone that doesn't plan their long flight with at least a 5 mile cushion, is asking for trouble. JJ Sinclair |
#50
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On Sat, 30 Aug 2003 19:13:47 +0100, Mike Lindsay
wrote: In article , Gene Nygaard writes On 27 Aug 2003 20:30:05 GMT, (JJ Sinclair) wrote: John Lee wrote. Nowhere! However on the equator 1 second of longitude equals 1 nautical mileWe also have 90 degrees between the equator and either pole. The equator is always 0 degrees and the poles 90 degrees. But in between, there are at least three different ways of measuring latitude: geocentric latitude (the angle formed at the center of the Earth), geodetic latitude (the one normally used, the angle formed between the line normal to the tangent of the ellipsoid and the axis of rotation), and the angles used in the parametric formulas representing an ellipse. These don't agree with each other at any place not on the equator or the poles. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ Hmm, interesting... What would the error be over, say 500km, if you used geocentric instead of geodetic measurement? In other words, does it matter? If you are measuring the difference between two points, it will make no difference whatsoever--assuming that you do the calculations properly for the angles you are using. It's just that those two end points will be at different latitudes, depending how you measure that latitude. That assumption has no guarantee of likelihood, if you are unaware that there are different ways to measure latitude. It's sort of like the Mars Climate Orbiter-turned-Crash-Lander. Those NASA engineers could have converted pound force seconds to newton seconds--only problem was, they didn't realize that they should be doing so. Gene Nygaard http://ourworld.compuserve.com/homepages/Gene_Nygaard/ |
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