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

Wed Aug 12 12:32:17 BST 2009

Mark Burton wrote:
> 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
>
>   
I think actually the reason for routing to work better with 3 instead of 
simply no argument might be, that garmin would not crash on very short 
arcs, but simply avoids to change roads often, so by setting 3 or higher 
one could actually reduce some unneccessary street changes, hence 
sometimes (very rare) better routing over long distances.

Probabely this issue that was a bit controlled by the patch, should be 
addressed by other patches however....
Until we have those patches, I am a bit sceptical about dropping the 
support to specify the arc length.
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
>   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.mkgmap.org.uk/pipermail/mkgmap-dev/attachments/20090812/764d2562/attachment.html