[mkgmap-dev] Still problems with remove-short-arcs

Wed Oct 30 16:39:52 GMT 2013

Hi all,

attached is a patch that detects "wrong" angles in roundabouts and
overwrites them with reasonable values. 
The typical angle in a roundabout is ~210°, it seems that Garmin
likes values between 180° and 240°, and refuses to use other
angles, at least on primary roads.

Compiled binary based on trunk r2794 is here:
http://files.mkgmap.org.uk/download/160/mkgmap.jar

tweezeRoundaboutArcs_v1.patch
<http://gis.19327.n5.nabble.com/file/n5783403/tweezeRoundaboutArcs_v1.patch>  

Note that this patch doesn't change the rendering data,
so ugly roundabouts will still look the same.
The corresponding patch is work in progress.

Gerd

GerdP wrote
> Hi Carlos,
> 
> just to clarify: You say that   remove-short-arcs=0 introduces the sharp
> angle.
> This is not true, as remove-short-arcs=0 will not move anything.  In fact,
> the sharp angle is caused by the rounding to Garmin map units.
> The green line in the screen shot shows the line that is used after
> rounding. You see that the rounding introduces an angle of ca. 75°.
> So why does rsa=3 help? Because it flatens the angle as it removes 
> one point. You can get the same effect if you move one of the node
> 975733410 a little bit.
> The problem disappears when I add a few lines in the code to make to sure
> that the calculated bearings are closer to reality (means I overwrite the
> values).
> I thought that the check-roundabout or adjust-turn-headings options were 
> meant to do that, but they don't seem to help.
> I think the reason is that adjust-turn-headings doesn't treat roundabouts
> special. 
> I see two possible solutions when 
> we detect the situation that the rounding has created an angle which is
> too sharp
> to be reasonable in a roundabout:
> 1) Overwrite the calculated heading values 
> 2) Try to find the point that was probably rounded wrong, and change its
> coordinates. This would have to be done much earlier in the chain.
> 
> Both will fix routing , but only 2) will help regarding the ugliness
> of the displayed roundabout. I try to code option 2), maybe both are
> needed because some roundabouts in OSM are divided into small
> fragments.
> 
> Gerd
> 
> Date: Sun, 27 Oct 2013 19:09:43 +0100
> From: 

> cdavilam@

> To: 

> mkgmap-dev at .org

> Subject: [mkgmap-dev] Still problems with remove-short-arcs
> 
> I still get some wrong routing at some roundabouts using 
> remove-short-arcs=0. See attached screenshots.
> At http://osm.org/go/b_YMZ7sDP-- MapSource makes a detour to avoid the 
> roundabout, due to a sharp angle that is introduced by 
> remove-short-arcs=0. If I use rsa=3, the route goes through the 
> roundabout, but the exit number is wrong, because the incoming road and 
> the first street are joined at the same node of the roundabout.
> 
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> 
> carlos.png (151K)
> &lt;http://gis.19327.n5.nabble.com/attachment/5783138/0/carlos.png&gt;

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