[GraphHopper] Does Graphhopper merge ways with equal flags and name?

[Jan Torben Heuer]

Hi Peter,

As I already mentioned earlier, I have a custom FlagEncoder that imports only a subset of osm ways. It imports only very few ways with only ~10 different flags overall. My assumption was now I could somehow get a graph from intersection to intersection (or at flags changes) but of course the names differ often between intersections (keep in mind that most edges are dropped, so there are not many intersections left). Hence names were my first guess where to start.

I only need the graph. It has nothing to do with the (graphhopper) routing.

Jan


Am 03.06.2015 um 10:52 schrieb Peter <graphhopper at gmx.de>:

> Hi Jan,
> 
> > Do you have a suggestion how I could do that?
> 
> That won't be easy without knowning what you intend to do. E.g. barriers, different speeds or changing flags due to changed tagging on the street: all will lead to 2 degree nodes. Different names is probably only a minor thing as streets change names 'in the middle of a street'.
> 
> A simple post-processing procedure for your case could be to create additional direct edges from junction to junction where you found a 2 degree node and mark the other edges as inaccessible.
> 
> Kind Regards,
> Peter
> 
> On 03.06.2015 10:24, Jan Torben Heuer wrote:
>> Hi Peter, 
>> 
>> If there is already a merging logic, then I would  ‚only‘ have to disable the name parsing or nameIndex? Do you have a suggestion how I could do that? (If that is too difficult I could also remove all name tags from the osm file, I think).
>> 
>> Just to be clear, my question has nothing to do with saving memory and stuff. That topic was brought up by ZhiQiang ZHAO. I just need a graph with edges from intersection to intersection.
>> 
>> Thanks,
>> 
>> Jan
>> 
>> 
>> Am 03.06.2015 um 09:09 schrieb Peter <graphhopper at gmx.de>:
>> 
>>> Hi Jan,
>>> 
>>> we do this kind of 'merging' logic already in the import step when deciding what should be handled as tower node and what is a pillar node. Otherwise you'll need as twice as many RAM when copying from one graph to the other.
>>> 
>>> 
>>> > Have you made a experiment to count the number of 2 degree nodes with the equal flags and name in OSM?
>>> > And then we can know how many edges we can save.
>>> 
>>> Yes, this should be done before implementing it :)
>>> 
>>> And as the merging logic is currently not 100% optimal, there could be some minor savings even when recognizing the different street names, but I'm unsure if it is worth the effort.
>>> 
>>> Issues like #234 or #111 will probably make more difference.
>>> 
>>> Kind Regards,
>>> Peter
>>> 
>>> On 02.06.2015 22:35, John Zhao wrote:
>>>> Hi,
>>>> 
>>>> AFAIK, there is no this kind of merging logic here.
>>>> Wait the answer from Peter.
>>>> Probably you need to implement it by your own.
>>>> And it's not easy. 
>>>> Maybe can be done before import?
>>>> What you want, is actually convert a tower node to a pillar node.
>>>> 
>>>> 
>>>> Best Regards,
>>>> ZhiQiang ZHAO
>>>> 
>>>> On Tue, Jun 2, 2015 at 1:27 PM, Jan Torben Heuer <jan at komoot.de> wrote:
>>>> Hi ZhiQiang ZHAO,
>>>> 
>>>> Thanks for your quick answer.
>>>> I have a custom FlagEncoder that imports only very few ways and I don’t need the names. I guess, I have mostly nodes with a degree of two.
>>>> 
>>>> Jan
>>>> 
>>>> Am 02.06.2015 um 21:53 schrieb John Zhao <johnthu at gmail.com>:
>>>> 
>>>>> Hi,
>>>>> 
>>>>> Have you made a experiment to count the number of 2 degree nodes with the equal flags and name in OSM?
>>>>> And then we can know how many edges we can save.
>>>>> 
>>>>> I doubt this should be not too much for OSM.
>>>>> 
>>>>> Best Regards,
>>>>> ZhiQiang ZHAO
>>>>> 
>>>>> On Tue, Jun 2, 2015 at 11:59 AM, Jan Torben Heuer <jan at komoot.de> wrote:
>>>>> Hi,
>>>>> 
>>>>> Can Graphhopper merge two ways with equal flags and name if there is no intersection between them (no third way connected)?
>>>>> 
>>>>> I would like to create a very reduces graph with only few edges. What would be the easiest way to achieve it? I think I would have to disable the nameIndex for instance.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> Jan
>>>>> 
>>> 
> 
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