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[mkgmap-dev] [PATCH v2] - round coordinates when zoomed out

From Felix Hartmann extremecarver at googlemail.com on Sat Nov 21 20:36:07 GMT 2009

Mark Burton wrote:
> Hi Felix,
>> Can't notice any difference to v1.
> OK - thanks.
>> BTW - Is it possible that there is a difference with the douglas peucker 
>> filter whether a road is routable or not?
> Yes, looking at the code, it seems that it doesn't change points that
> are routing nodes so routable ways will be "less smooth" than
> non-routable ways.
yeah - the problem is not really one being smoother than the other, but 
the ways being different. So if I use the multiple_elements_patch only 
one "line" will be routable, whereas the copies are not routable. As I 
wan't to display the ways side-by-side the further one zooms out, the 
more the ways are apart from each other, or overlapping. At resolution 
22 this effect is barely noticeable, on 20 it is okay, but on 18 it 
really gets distracting. Also roads running parallel to rivers often get 
inside the river because of this. For me in practice on bicycle/mtb/foot 
this does not matter much because I rarely use resolution 20 or lower, 
but I assume that for carrouting on a motorway it would be nicer to have 
all ways "smoothed" the same. Might be a bit difficult to change however 
I think, because this would need additional calculation time for non 
routable ways to know which nodes would be routing nodes in case a line 
is not routable.
>> I think it is possible that non routable ways are smoothed heftier than 
>> routable ways. This has nothing to do with this patch though, but the 
>> difference only seems to become really visible on resolution <20
>> (maybe resolution 24 is filtered if not routable, but not filtered if 
>> routable. Then the more filtering is applied on each successive level, 
>> the bigger the difference).
> It think the DP filter does nothing at res 24 whether the way is
> routable or not.
>> Also I noticed that cgpsmapper maps, seem to have much higher smoothing 
>> at lower resolutions compared to mkgmap (using 2.6). At resolution 24 
>> and 22 it seem to be mostly identical though. Maybe we could also 
>> increase the douglas peucker severity on resolution <20 compared to 
>> right now. Even with very few lines mkgmap maps seem slow on GPS on 
>> resolution 16 or 18.
> That's worth experimenting with. 
> Perhaps Johann can comment on this, he's the original author of the DP
> stuff.
> Cheers,
> Mark
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