On Mon, 12 Jan 2004 09:38:56 +1030, Mark Newton wrote > On Mon, Jan 12, 2004 at 08:53:37AM +1000, Jason Armistead wrote: > > > In any case, the points that are used as reference points might > not be the > same as the ones accepted as turnpoints, some of which > are, for example, > terminal buildings, or simply runway intersections. > > I think we started talking about this from the context of final-glide > planning, yes? > > If the few feet of height difference inherent in moving the aerodrome > reference point from one place in the paddock to another actually > matters, might I submit that you're cutting your margins a bit too > fine...? :-) On Mon, 12 Jan 2004 09:38:56 +1030, Mark Newton wrote > On Mon, Jan 12, 2004 at 08:53:37AM +1000, Jason Armistead wrote: > > > In any case, the points that are used as reference points might > not be the > same as the ones accepted as turnpoints, some of which > are, for example, > terminal buildings, or simply runway intersections. > > I think we started talking about this from the context of final-glide > planning, yes? > > If the few feet of height difference inherent in moving the aerodrome > reference point from one place in the paddock to another actually > matters, might I submit that you're cutting your margins a bit too > fine...? :-)
Mark No attempt whatsoever to make VERY marginal final glides - anyone who knows me would know that I've NEVER taken that approach with my flying. I want to arrive with a few thousand feet of air between me and the ground, and not to skip in over the fench after a straight-in approach. With regard to my posting, I am more interested in identifying whether a turnpoint database should be based on arbitrary points like aerodrome reference points (ERSA co-ordinates) or aerodrome features, or a mixture of both. If you are still using turnpoint photography for claiming a badge flight, you need to have whatever readily identifyable point in view and be in the right observation zone. This is probably going to be some airfield feature, be it a building, runway intersection, or whatever. If you are using a GPS-equipped flight recorder, you just want to go around the point by an appropriate margin based on its co-ordinates. I would prefer to look down and say "there it is" as I round some identifyable feature which corresponds to my GPS turnpoint co-ordinates also. Our CFI, Clive Potter, who at one stage was Certificates Officer for GFA, tells me that the ground features were worked out from topographical maps, most often accurate to around (if I recall our conversation correctly), something like 10 seconds, which works out at around +/- 300m. If someone was trying to claim a marginal flight, like 301 km for a 300km badge, then he'd rather reluctantly have to consult more accurate maps to identify the features in question more precisely. In his day, the list of turnpoints numbered around a few thousand, and it was all passed on to the next Certificates Officer at the conclusion of his tenure. I am just trying to arrive at a turnpoint database (mainly for NSW, where I fly, but happy to enter ERSA data from elsewhere) which has: (a) Accurate lat/lon co-ordinates (b) Accurate elevations (c) Easily recognisable visual markers Whether you're using a handheld GPS, flight computer, turnpoint camera or a paper list of turnpoints, or a combination of these, you should have some degree of faith in your navigation data. When I've using a flight computer, it makes sense to expect accurate elevations for all the points, and not necessarily just the airfields. Why do have a job of the database ? If we have accurate sources of data to hand from visitations with GPS units, we might as well use those rather than relying on approximations derived from reading paper maps. At the moment, no-one seems to be able to categorically say where the data in the "well known" sources like the WorldWide TurnPoint Exchange originated from, and how accurate it is. Jason _______________________________________________ Aus-soaring mailing list [EMAIL PROTECTED] http://lists.internode.on.net/mailman/listinfo/aus-soaring
