[mkgmap-dev] help needed

Fri Aug 1 15:12:38 BST 2014

Hi Lambertus,

thanks again. I want to solve this problem:
In mkgmap we have to calculate the great-circle distance very often, 
as well as the cross track error.
We need the values for all kinds of algos (nearest point, DP-Filter, 
WrongAngleFixer etc.), not just for the img itself.
Up to now we use those formulas which are fastest,
but as we saw they do not always work. 
So I want to find a simple algo to decide whether the fast
formula is good enough.
Always using the highest precision would slow down mkgmap
by ~30 %.

Gerd

Lambertus wrote
> I'm not sure if it is of any help, but with http://yournavigation.org 
> (which also uses OSM) you can specify which distance algorithm to use. 
> It uses this PHP class for the calculations:
> https://github.com/treffynnon/Geographic-Calculations-in-PHP
> 
> Available methods:
> Vincenty
> Simplified great circle
> Haversine
> Cosine
> 
> Add a &v= parameter to the request to choose the algorithm:
> http://wiki.openstreetmap.org/wiki/YOURS#Parameters
> 
> /offtopic: I see YOURS should be upgraded with the new class...
> 
> 
> On 31/07/2014 18:21, Andrzej Popowski 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/
>>
> 
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