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On Tue, 25 Nov 2003 22:37:33 +0000, Tim Newport-Peace
] wrote: I don't think it happens quite that way. If you submit a recorder that does not conform the Specification in Force at the time, approval will not be granted until it DOES conform. The specification would need to be changed FIRST. As opposed to NOT approving a recorder which does meet the specification at the time and then changing the specification later? Which GFAC has done. I do not believe that the requirement for Barometric Altitude will be removed any time soon. I agree, that would be far too sensible a decision for IGC/GFAC to make. Mike Borgelt |
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I agree with your analysis in principle, but I dont *know* that WAAS works
like this. In any case I dont see any point in the enhanced accuracy of WAAS for glider flights. The errors in the normal GPS signals are already small enough. I just dont want to see an 'improvement' leading to yet another unforseen problem. -- Regards, Adrian Jansen J & K MicroSystems Microcomputer solutions for industrial control "Bruce Hoult" wrote in message ... In article , "Adrian Jansen" wrote: You might want to consider the implications of WAAS. I have no direct experience, but the principle is that you take an external signal and use it to 'correct' the GPS location to another place - hopefully more accurate. But what is to stop you sending bogus 'corrections' and making the GPS think its somewhere else entirely ? The WAAS signals are much easier to generate than the original GPS satellite signals. Sounds an easy way to cheat to me. But how far can the WAAS signal "correct" the GPS one? I assume the principle is that the transmitter knows exactly where it really is, so if GPS says it is somewhere else then the difference is an error which will apply to all other GPS receivers in the area. Since the GPS error is likely to be on the order of 5m - 10m, and very very unlikely to be more than a couple of hundred meters, I would expect the system to be designed to correct the GPS positions by no more than a few hundred meters. Another characteristic is that the correction is the same not only for a reasonably large geographic area, but that the necessary correction changes quite slowly, over a period of many minutes. If I was designing the system, I expect I would also take advantage of that to reduce the amount of information that need to be transmitted. So I would expect a maximum correction possible of, say, less than a km, and rapid changes to the correction to be either impossible or else rather unusual and therefore suspicious. I don't see how you could use that to make any significant difference to a glider flight. -- Bruce |
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