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

Mon Mar 5 13:33:30 GMT 2012

Hi Steve,

If I got you right, you think that the patch is ok but the maps produced
with the 
trunk version might contain completely wrong values. 
I have no idea how one can find out what's right or wrong. Probably a
comparison 
between garmin map data and our results?

Gerd

Steve Ratcliffe wrote
> 
> Hi
> 
>> okay, safety first. Maybe Steve can say more about how important the
>> precision
> 
> It ultimately fits into a byte, so it is only accurate to about 1.5
> degrees anyhow. I only saw a difference for the value 90 degrees
> when I tried WanMil's patch. But both are wrong in that they are only
> 179 degree apart instead of 180. Why not just reverse the integer
> value instead of suffering more rounding with floats?
> 
> However I am not convinced that the original code is correct
> in what it is doing.
> 
> 
> If you have a road like this:
> 
>     B
>     .-------. C
>     |        \
>     |         \
>     |          \
>     |           \
>     |            * D
>     |
>     *
>     A
> 
> where * are routing nodes, and . are plain nodes.
> 
> I thought that there were two directions, the initialHeading and the
> Bearing. The initialHeading was AB and the Bearing AD. (For the
> forward arc ABCD, for the reverse arc that would be DC and DA)
> 
> However the code has initialHeading and finalHeading of AB and CD
> if I am reading it correctly.
> 
> I could be wrong of course, since I only looked at the routing network
> very early on, and I'm not sure where this memory came from, since I
> never implemented the complex cases.
> 
> ..Steve
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> mkgmap-dev at .org
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> 

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