[mkgmap-dev] help neededFrom GerdP gpetermann_muenchen at hotmail.com on Fri Aug 1 11:16:14 BST 2014
Hi all, I think my problem is solved. JOSM doesn't display the so called great circle which is the shortest line between two points on a spere. I am not sure what exactly JOSM displays, but obviously I can't use it to verify the calculations. Thanks for the hints! Gerd GerdP wrote > Hi Bill, > >> I tried to confirm a couple of things, and ran out of time, but thought >> the ideas might be of use to you. >> 1) Are you sure that both the algorithm and JOSM are drawing the same >> line between LAX and JFK. For example, one could be using a great >> circle route, and the other using a direct heading. This would result >> in a different distance between A and the line. > > I think JOSM does it right. > >> 2) Have you tried using a two points for the reference line that are >> directly North/South of each other, or on the equator as these should >> result in the reference line being the same regardless of the method of >> determining it. > > Good idea! I thought I did that before, but maybe with wrong values. > I found that the formula (or my implementation) is wrong. > Now I can try to find the reason... > > Gerd > >> >> Bill >> >> p.s. Thank you, and everyone else who is continuing to improve and >> support mkgmap. >> >> >> On 07/31/2014 09:41 AM, GerdP wrote: >> > Hi Andrzej, >> > >> > thanks for the hints, I'll have a look at them tomorrow. I think >> > "Spherical versus ellipsoidal model" as a reason is unlikely, the >> difference >> > should >> > be < 1 %, not ~50% >> > Today I looked at various webpages which calculate the distance between >> > two points, e.g. airports. It is quite funny how different the results >> are, >> > probably because some are using R=6371 km and others 6378.135 m or >> > values between. >> > >> > Gerd >> > >> > >> > >> > popej wrote >> >> Hi Gerd, >> >> >> >> I have looked at your example file in QGIS and Global Mapper and they >> >> show distance like JOSM. I don't know why there is so big difference. >> My >> >> guess is that it could be caused by spherical versus ellipsoidal model >> >> of the Earth. Maybe you could test algorithms based on Vincenty's >> >> formulae? See for example: >> >> >> >> >> http://www.gavaghan.org/blog/free-source-code/geodesy-library-vincentys-formula-java/ >> >> >> >> http://geographiclib.sourceforge.net/html/java/ >> >> >> >> -- >> >> Best regards, >> >> Andrzej >> >> _______________________________________________ >> >> mkgmap-dev mailing list >> >> mkgmap-dev at .org >> >> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev >> > >> > >> > >> > >> > -- >> > View this message in context: >> http://gis.19327.n5.nabble.com/help-needed-tp5813164p5813323.html >> > Sent from the Mkgmap Development mailing list archive at Nabble.com. >> > _______________________________________________ >> > mkgmap-dev mailing list >> > > mkgmap-dev at .org >> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev >> >> _______________________________________________ >> mkgmap-dev mailing list >> > mkgmap-dev at .org >> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev > > _______________________________________________ > mkgmap-dev mailing list > mkgmap-dev at .org > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev -- View this message in context: http://gis.19327.n5.nabble.com/help-needed-tp5813164p5813383.html Sent from the Mkgmap Development mailing list archive at Nabble.com.
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