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-form...
http://geographiclib.sourceforge.net/html/java/
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