Gerd,
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.
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.
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
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