[GraphHopper] question on contraction

[Renaud De Landtsheer]

Le 7/05/2014 16:32, Peter K a écrit :
>> When the lazy updates are activated,
>> * do we still need to update the neighbour points of a node we just
>> contracted?
> Lazy update is exactly for that purpose: updating the priorities of the
> neighbour nodes of a contracted node

as far as I understand it, lazy update is about checking that the node 
we are going to contract has a proper priority by recomputing its 
priority, and postponing its contraction if necessary. It does not seem 
to be about updating the neighbours of a node that has just been updated.
>> * is it still needed to perform periodic updates of all the priorities?
> we only do periodic updates for not yet contracted nodes

yes, but I feel that the lazy updates actually performs a redundant 
function with the periodic updates.

>
> Keep in mind: all the ordering and preparation procedure is entirely
> heuristic nature. But still it leads to an algorithm with correct
> behaviour, no heuristics. The only difference e.g. if we don't do lazy
> or periodic updates etc is the quality of how fast is the query, how
> fast is the preparation itself and how many shortcuts were produced.

Yes, I understand, I just want to make contraction faster without losing 
on quality,
hence my remarks

>
> Peter.
>
>
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-- 
*Renaud De Landtsheer, Ir, Phd*
Senior R&D Expert
CETIC
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