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

Sat Nov 21 20:26:42 GMT 2009

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.

> 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