NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Call for Hands
From: Tom Feuerhelm
Date: 1999 Mar 10, 17:13 EST
From: Tom Feuerhelm
Date: 1999 Mar 10, 17:13 EST
Dear ALL, When I read that Call for hands, I could no longer resist from answering!! YES, THERE ARE INDEED more people watching closely all of your discussions and deliberations! Some of them only have little time.... When you call for HANDS, i myself could, because of lots of other things to be done, at this moment only offer my FEET, and it is very difficult to do the necessary trig an HO and DR and SOG and so on with feet only ;-)) Seriously, I do enjoy and learn a lot from all those discussions, therfore, please do not despair and keep the thing going!!! Maybe I should pose a few questions which have bothered me for quite some time, which i somehow discovered in silicon sea more than a year ago, but i somehow lost trace of it: ----------------------------------------------------------------- - Sailing on the Chart, we use Mercator Projection, right? Now I found out that for some countries, they use different formulae for the "Mercator Bit": - US uses an ellipse (one or another "Correction" to the main part of the formula) as model of the earth. - In Germany, at least the navigation "hobbyists" use the formulae which correspond to a sphere (no ... additions to the "main" formula). - I dont know much about other countries, but at least there seem to be more and different "Mercator Projections" floating around, for example for geodetic (??) purposes like actual chart making. Now comes the problem: - In Silicon Sea i learned a few years ago, that the american use of an ellipse-model would be more precise (as you can also find out when you look at a GPS display, where "Chart Datum" is very improtant), which caused me some headaches to squeeze both versions into a spreadsheet for solving silicon sea problems. BTW, I have found that working german navigation exam problems with those "ellipse type formulae" would produce errors which could result to a FAIL in an actual test, therefore, those differences are at least somewhere important... - However, in astronavigation, we all use a spherical model ! 1) Does that make sense instead of being more simple for calculation ? 2) Has anybody ever tried to evaluate the deviations / errors produced when using those different formulae (I would suspect those differences to be negligible, but one never knows....) 3) Are there any programs out there to make printouts for plotting sheets in which you could adjust for the different formulae, and would that make sense at all ? 4) Would we not, at least in principle, have to correct positions obtained by astronavigation to the correct chart datum to the chart which is used on the ship ? Can anybode help me out of this mess? Maybe some of you will judge my "problem" to be nonexistant, but I feel it to be quite annoying, when a science and art like navigation would depend on "country" and "politics" :-)) My very best regards to all, AND keep up the good work! Tom Feuerhelm ?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?? ? TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX: ? ? navigation ? ?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-??