[mkgmap-dev] Option --remove-short-arcs

Wed Aug 12 12:26:37 BST 2009

Hi Felix,

> Mark Burton wrote:
> > Hi Steve,
> >
> >   
> >> Is there any problem with this option, such that you might not want
> >> to use it?
> >>     
> >
> > I am not aware of any problem.
> >  
> >   
> >> As I understand it, if you do not give it then routing will not work,
> >> as we know (or believe) that all routing arcs have to be more than 5.4m.
> >>     
> >
> > I believe that the mimimum distance will depend on lat/lon because the
> > real constraint is that the source and target nodes must not have the
> > same coordinates (resolution being 360 deg / 2^24)
> >
> >   
> >> If that is so, then we should just set the required behaviour whenever
> >> the route option is given.
> >>     
> >
> > Why don't we do that but still provide an option to turn off the
> > short arc removal (which should never need to be used but may be useful
> > when tracking down problems).
> >
> >   
> >> I realize that there might be other approaches, eg we could stretch arcs
> >> instead of removing them, but if removing them is our current best 
> >> approach, lets make it the default.
> >>     
> >
> > It seems to be working well enough at the moment.
> >
> > Shall I change the code to remove the --remove-short-arcs option and,
> > instead, enable that function if --route is specified and
> > (the new) --keep-short-arcs option is not specified?
> >
> > Cheers,
> >
> > Mark
> >   
> Yes, but we should be clear about the distance needed. I used =3 because 
> without specifying it, I had some route calculation working, that 
> without specifying did not work. If there is really 5.4m then the 
> default should go for 5.4 -- or just leave the option as it is right now 
> but use it by default except if say --remove-short-arcs=no is given...

Ahh, I forgot about that aspect. At this time, if you don't specify a
length with the --remove-short-arcs option, it only removes zero-length
arcs. I think that is the most sensible behaviour because we know that
zero-length arcs are bad for routing. The fact that some maps require a
minimum arc length to be specified should be investigated some more to
see what the issue is. 

Cheers,

Mark