[mkgmap-dev] [Patch] Reduce bearingTo() calculations

Sun Mar 4 21:08:23 GMT 2012

I don't know what's happening with the results of the bearing 
calculations. So as long as the results differ I don't want to commit 
that without a solid explanation that this is ok.

WanMil

> Hi WanMil,
>
> the calculation in bearingTo() involves a lot of rounding errors because of
> the trig. functions.
> I verified that no value differed more than 0.5, which is good enough for us
> since we only use the
> integer value.
> See also http://www.movable-type.co.uk/scripts/latlong.html
> It says:
> "For final bearing, simply take the initial bearing from the end point to
> the start point and reverse it (using θ = (θ+180) % 360)."
>
> That's what I tried to implement.
>
> Gerd
>
>
> WanMil wrote
>>
>> Hi Gerd,
>>
>> I have checked your patch by comparing old bearing to results with new
>> results. I got lots of differences as you can see by trying attached
>> patch.
>>
>> Can you please carefully check why there is a difference and which
>> version is 'better'?
>>
>> WanMil
>>
>>
>>
>>> Hi,
>>>
>>> in class RoadNetwork we calculate both p1.bearingTo(p2)  and the reverse
>>> p2.bearingTo(p1).
>>> I think the reverse value should be calculated from the initial value.
>>>
>>> See attached patch.
>>>
>>> Gerd
>>>
>>> http://gis.19327.n5.nabble.com/file/n5533880/bearingTo.patch
>>> bearingTo.patch
>>>
>>> --
>>> View this message in context:
>>> http://gis.19327.n5.nabble.com/Patch-Reduce-bearingTo-calculations-tp5533880p5533880.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
>>
>
>
> --
> View this message in context: http://gis.19327.n5.nabble.com/Patch-Reduce-bearingTo-calculations-tp5533880p5535815.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