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

Sun Mar 4 21:25:28 GMT 2012

Hi WanMil,

okay, safety first. Maybe Steve can say more about how important the
precision 
is. It is rounded again later and then writen to the *.img file. I assume
that it is 
not a problem when the value differs a little bit.

Gerd

WanMil wrote
> 
> 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
>>>>
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>>
>>
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