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

[John Zhao]

Hi Peter,

I am more confused.
I think the original question is:
If there are 2 different OSMways in original OSM data, they and only they
are connected.
And all the other tags are the same.
Does Graphhopper will merge them into a single edge in GH?
Then the graph is a little bit simplified.

*Best Regards,*
*ZhiQiang ZHAO*

On Wed, Jun 3, 2015 at 2:07 PM, Peter <graphhopper at gmx.de> wrote:

>  Hi John,
>
> good question :)
>
> Maybe that is the reason that in rare cases pillar nodes are incorrectly
> determined as tower nodes. One could introduce a new PILLAR_NODE2=0
> variable and try if everything is still working. But before I would pick a
> big area and count the percentage of those incorrectly determined tower
> nodes if this is valuable at all.
>
> Regards,
> Peter
>
>
>
> On 03.06.2015 22:16, John Zhao wrote:
>
> Hi Peter,
>
>  That sounds reasonable. But I am still confused.
> I think the logic is under the below logic.
> Based on the logic and commets, a node is "mark node as tower node as it
> occured at least twice times", not "at least 3 times".
>
>     void prepareHighwayNode( long osmId )
>
>     {
>
>         int tmpIndex = getNodeMap().get(osmId);
>
>         if (tmpIndex == EMPTY)
>
>         {
>
>             // osmId is used exactly once
>
>             getNodeMap().put(osmId, PILLAR_NODE);
>
>         } else if (tmpIndex > EMPTY)
>
>         {
>
>             // mark node as tower node as it occured at least twice times
>
>             getNodeMap().put(osmId, TOWER_NODE);
>
>         } else
>
>         {
>
>             // tmpIndex is already negative (already tower node)
>
>         }
>
>     }
>
>  *Best Regards,*
> *ZhiQiang ZHAO*
>
> On Wed, Jun 3, 2015 at 12:15 PM, Peter <graphhopper at gmx.de> wrote:
>
>>  Hi,
>>
>> the details are a bit trickier as we do everything very memory efficient.
>>
>> And if a osm node occurs twice it is a pillar node, otherwise it is a
>> tower node.
>>
>> Kind Regards,
>> Peter
>>
>>
>> On 03.06.2015 21:05, John Zhao wrote:
>>
>> I go through the logic:
>> It go through all osmways, and count the occurrence of nodeID.
>> if nodeID appear only once, it's a pillar node.
>> otherwise, it's a tower node.
>>
>>  That's it. Do I miss something?
>>
>>
>>  *Best Regards,*
>> *ZhiQiang ZHAO*
>>
>> On Wed, Jun 3, 2015 at 11:55 AM, Peter <graphhopper at gmx.de> wrote:
>>
>>>  Hi,
>>>
>>> there is no separate merging logic (although there was in 0.1 or
>>> something). In OSMReader it is decided when an edge is created and e.g. OSM
>>> ways are splitted if there are barriers or junctions on the way. So it
>>> decides whether an osm nodes will be a tower node or just a pillar node
>>>
>>> Regards,
>>> Peter
>>>
>>>
>>> On 03.06.2015 20:35, John Zhao wrote:
>>>
>>> Hi Peter,
>>>
>>>  Could you tell me where is the merging logic?
>>> That's interesting.
>>>
>>>  *Best Regards,*
>>> *ZhiQiang ZHAO*
>>>
>>> On Wed, Jun 3, 2015 at 12:09 AM, Peter <graphhopper at gmx.de> wrote:
>>>
>>>>  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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