[GraphHopper] Does Graphhopper merge ways with equal flags and name?
John Zhao
johnthu at gmail.com
Wed Jun 3 22:14:43 UTC 2015
Hi Peter,
Thanks for the explanation.
I think the answer is:
there is no merging logic to combine 2 different but connected OSM ways in
GH.
GH only chop the long OSM ways into several edges by the intersections.
*Best Regards,*
*ZhiQiang ZHAO*
On Wed, Jun 3, 2015 at 2:27 PM, Peter <graphhopper at gmx.de> wrote:
> Hi John,
>
> the problem is as follows:
> Assume the osm ways A-B-C (west to east) and D-E-F (north to south)
>
> Now if the node B is the same as F or E then we have a tower node or
> junction. But if the nodes C and F are identical then this would be a
> pillar node (and we handle it like a tower node). So the import always
> assumes case 1 and we are always safe but in some rare cases we could avoid
> creating a tower node.
>
> Regards,
> Peter
>
>
> On 03.06.2015 23:13, John Zhao wrote:
>
> 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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