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<body class='hmmessage'><div dir='ltr'>Hi Bill,<br><br>> I tried to confirm a couple of things, and ran out of time, but thought <br><div>> the ideas might be of use to you.<br>> 1) Are you sure that both the algorithm and JOSM are drawing the same <br>> line between LAX and JFK. For example, one could be using a great <br>> circle route, and the other using a direct heading. This would result <br>> in a different distance between A and the line.<br><br>I think JOSM does it right.<br><br>> 2) Have you tried using a two points for the reference line that are <br>> directly North/South of each other, or on the equator as these should <br>> result in the reference line being the same regardless of the method of <br>> determining it.<br><br>Good idea! I thought I did that before, but maybe with wrong values.<br>I found that the formula (or my implementation) is wrong.<br>Now I can try to find the reason...<br><br>Gerd<br><br>> <br>> Bill<br>> <br>> p.s. Thank you, and everyone else who is continuing to improve and <br>> support mkgmap.<br>> <br>> <br>> On 07/31/2014 09:41 AM, GerdP wrote:<br>> > Hi Andrzej,<br>> ><br>> > thanks for the hints, I'll have a look at them tomorrow. I think<br>> > "Spherical versus ellipsoidal model" as a reason is unlikely, the difference<br>> > should<br>> > be < 1 %, not ~50%<br>> > Today I looked at various webpages which calculate the distance between<br>> > two points, e.g. airports. It is quite funny how different the results are,<br>> > probably because some are using R=6371 km and others 6378.135 m or<br>> > values between.<br>> ><br>> > Gerd<br>> > <br>> ><br>> ><br>> > popej wrote<br>> >> Hi Gerd,<br>> >><br>> >> I have looked at your example file in QGIS and Global Mapper and they<br>> >> show distance like JOSM. I don't know why there is so big difference. My<br>> >> guess is that it could be caused by spherical versus ellipsoidal model<br>> >> of the Earth. Maybe you could test algorithms based on Vincenty's<br>> >> formulae? See for example:<br>> >><br>> >> http://www.gavaghan.org/blog/free-source-code/geodesy-library-vincentys-formula-java/<br>> >><br>> >> http://geographiclib.sourceforge.net/html/java/<br>> >><br>> >> -- <br>> >> Best regards,<br>> >> Andrzej<br>> >> _______________________________________________<br>> >> mkgmap-dev mailing list<br>> >> mkgmap-dev@.org<br>> >> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev<br>> ><br>> ><br>> ><br>> ><br>> > --<br>> > View this message in context: http://gis.19327.n5.nabble.com/help-needed-tp5813164p5813323.html<br>> > Sent from the Mkgmap Development mailing list archive at Nabble.com.<br>> > _______________________________________________<br>> > mkgmap-dev mailing list<br>> > mkgmap-dev@lists.mkgmap.org.uk<br>> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev<br>> <br>> _______________________________________________<br>> mkgmap-dev mailing list<br>> mkgmap-dev@lists.mkgmap.org.uk<br>> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev<br></div> </div></body>
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