[GraphHopper] Does Graphhopper merge ways with equal flags and name?
Peter
graphhopper at gmx.de
Wed Jun 3 21:07:56 UTC 2015
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
> <mailto: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
>> <mailto: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
>>> <mailto: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 <mailto: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 <mailto: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 <mailto: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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