# [mkgmap-dev] help needed

From Gerd Petermann gpetermann_muenchen at hotmail.com on Fri Aug 1 05:52:14 BST 2014

```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 lists.mkgmap.org.uk
> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
>
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