[mkgmap-dev] short arcs demystified, please try value 0

Sat Oct 5 13:25:45 BST 2013

El 05/10/13 11:56, GerdP escribió:
> Hi all,
>
> I think I understand now most of the miracles related to
> short arcs and I am pretty sure that we can solve
> the known problems without adding source complexity.
>
> 1) In 2009 Mark Burton added the
> remove-short-arcs option with r1049.
> 2) With r1060 he added the option to pass a parameter
> giving the minimum arc length to fix problems like
> "disappearing ways". Unfortunately, he missed the
> real reason for the error, which IMHO was the
> buggy implementation of --link-pois-to-ways
> and --remove-short-arcs regarding the
> highway count causing more or less
> unpredictable results.
> 3) For four years people wondered what value to use
> as a change of the value was likely to
> "fix" a known routing error while also adding
> other "not yet known" errors.
>
> Today I've committed r2736.
> I my eyes (presuming all coding errors are fixed now)
> the only usable value is --remove-short-arcs=0,
> everything else is likely to
> create problems like distorted lines, wrong
> routing (cars routed through footways)
> and wrong exit hints in roundabouts.
> The only advantage that I see is a slightly smaller
> number of nodes, but this will soon be fixed
> when the mergeroads branch is merged to trunk,
> but I might have missed something.
>
> So, in short:
> All those that are using mkgmap to create routable
> maps, please try r2736 with --remove-short-arcs=0
> (binary is here http://files.mkgmap.org.uk/download/152/mkgmap.jar)
> or use the mergeroads branch (requires style changes)
> If you find any problem regarding routing, please
> let us know and try to provide details.
>
> If I hear no complains until Oct 15, I like to change the default
> back to 0 and print a warning if a different value is used.
> If --remove-short-arcs=0 works fine for everybody, we
> should remove the option.
>   
> Gerd
Thanks for the deep work you have done on it Gerd.
I have a roundabout test case where routing have been failing for a long 
time. With r2736 routing works fine with remove-short-arcs=0 and without 
any value (default), but the shape of the roundabout is a circle with 0 
and something like a start with default, so much better with 0.