On Sat, 17 Aug 2002 07:28:22 Pat Naughtin wrote: >Dear Marcus, Joe, and All, > >If I add Hayford's 'Equatorial circumference of the earth = 40 076.594 km' >and his 'Polar circumference of the earth = 39 941.028 km' and divide by 2, >does this give me the mean circumference of the Earth? In this case it would >be 40 008.811 kilometres - or some 9 kilometres more than the original >(1792) figure. > Thanks for the info, Pat. Now, I believe my question still has relevancy since it's still unclear how one came up with the above values. Did the authors consider earth's relief, sea level values, disregarded relief altogether, calculated at some arbitrary meridian?... Until we know what assumptions were used it's difficult to "check" the validity of the above results.
In any case, we could proceed to derive charts, cartography data, etc at some arbitrary altitude (such as at my 560 m value). This should not be such a pain for the community since we could quote altitudes at RL instead of SL (Reference Level and Sea Level, respectively). No big deal, really. >BTW, Marcus, where did you get the number '560 m below sea level'? > Simple, I assumed that the "correct" value at sea level was 40003.52 km (i.e. a value as quoted by another colleague here sometime ago). Found a radius of 6366.758 km. Now subtract this value at a radius that would give exacts 400000, i.e. 6366.198 and voil`, the value comes at 560 m below "sea level" (if that's what was used to derive the "correct value"). If one uses the nautical mile as referring to that (sea level), then the distance becomes a convenient 500 m! (well, ok... 510, 511...). The principle behind this calc could apply to any other value that is deemed to be the "sea level" one. Whatever the spherical difference in altitude this would become the RL where 0.01 gr would be exacts 1 km. Then, after doing this it would be a piece of cake to come up with GPS charts and whatnot using the 100 gr angle system. Current charts could undergo very simple updates with just a footnote to it indicating what RL is and all (except, of course, that these projections would refer to decimal grids...). All airports in the world would use such RL as reference, and no longer the SL. There would be no potential for confusion, the nautical mile trash would be history (and so would the hideous knot...) and presto! I hope this answered your question, Pat. Marcus >Cheers, > >Pat Naughtin CAMS >Geelong, Australia > >on 2002-08-17 01.18, Ma Be at [EMAIL PROTECTED] wrote: > >> Based on Joe's post below and other ones earlier shall we conclude that we >> still do not have the answer to the above question (in the subject)? >> >> Again, I launch the question what would prevent us from defining a specific >> diameter for purposes of navigation and cartography at some 560 m below sea >> level and use the principle of "relative" altitudes and all (like we already >> do with atmospheric pressure) to get rid of the nautical mile crap? >> >> Marcus >> >>>> J. F. Hayford reported to the International Geodetic and Geophysical Union >>>> in 1926 that; >>>> Equatorial circumference of the earth = 40 076.594 km, >>>> Polar circumference of the earth = 39 941.028 km. >>>> My source does not state whether these figures are for sea level, as seems >>>> likely, or if they take account of land and mountains. However, the >>>> uncertainty in the radius of the earth can not exceed 50 metres. That is, >>>> the uncertainty is only one part in 100 000. >>>> >>>> Joseph B.Reid... >> >> >> Is your boss reading your email? ....Probably >> Keep your messages private by using Lycos Mail. >> Sign up today at http://mail.lycos.com >> > > Is your boss reading your email? ....Probably Keep your messages private by using Lycos Mail. Sign up today at http://mail.lycos.com
