[GraphHopper] There must be bug on the subnetwork removal

Wed Jul 29 10:38:24 UTC 2015

Hi Peter,

The test case could be:

clique A ---> node c ---> clique B

Clique means SCC, like all connected graph.
node c is a SCC, if we assume a node can reach itself.

Actually, an extreme case could be:
node a ---> node b ---> node c

each node is a SCC.

*Best Regards,*
*ZhiQiang ZHAO*

On Wed, Jul 29, 2015 at 3:24 AM, Peter <graphhopper at gmx.de> wrote:

>  Hi ZhiQiang,
>
> the examples you show are SCC of only 1 node, but the original example is
> not a SCC I think, as you have an outgoing and an incoming edge. So I guess
> this is a bug or something. Maybe you can provide a failing and small unit
> test for this so that I can have a look?
>
> Also the step 4 is indeed only for informational purposes but will print
> new information if the step 3 changed the subnetworks.
>
> Regards,
> Peter
>
>
> On 29.07.2015 11:44, John Zhao wrote:
>
> Hi Peter,
>
>  There are a lot of SCC with only 1 node, like:
> http://www.openstreetmap.org/node/1707762331
>  http://www.openstreetmap.org/node/386885888
>  http://www.openstreetmap.org/node/364825950
>
>  Step 4 is only to findSubnetwork(), and print some info, not removal
> them.
> So, step 4 is optional.
>
>  Now I only understand why this happen. :(
>
>
>  *Best Regards,*
> *ZhiQiang ZHAO*
>
> On Wed, Jul 29, 2015 at 2:28 AM, Peter <graphhopper at gmx.de> wrote:
>
>>  Hi ZhiQiang,
>>
>> > And the http://www.openstreetmap.org/node/678314919 itself is a SCC.
>> size is 1.
>>
>>  It shouldn't be a SCC im my opinion - is there a bug?
>> If it is not a bug - do you have a suggestion for this, like avoiding
>> step 4?
>>
>> Regards,
>> Peter
>>
>>
>>
>> On 29.07.2015 11:18, John Zhao wrote:
>>
>> Hi Peter,
>>
>>  The parameter I set are minOnewayNetworkSize = 20, minNetworkSize = 200
>>
>>  on step 3, despite the node http://www.openstreetmap.org/node/678314919,
>> the inside island is a SCC, and the size is larger than 20.
>> So, this island is kept, instead of removal.
>> And the http://www.openstreetmap.org/node/678314919 itself is a SCC.
>> size is 1. Then it was removed.
>>
>>  Then on step 4, the island is recognized as a subnetwork, which has
>> size less than 200.
>>
>>  *Best Regards,*
>> *ZhiQiang ZHAO*
>>
>> On Wed, Jul 29, 2015 at 1:04 AM, Peter <graphhopper at gmx.de> wrote:
>>
>>>  Hi ZhiQiang,
>>>
>>> you mean the oneway procedure (step 3) removes nodes+edges leading to
>>> further normal subnetwork removal in step 4? This should not happen. The
>>> subnetwork should be removed already in step 3.
>>>
>>> > On step 2, although there is a gate
>>> http://www.openstreetmap.org/node/703042503
>>> > on http://www.openstreetmap.org/way/6374339
>>>  > And gate block that edge.
>>>
>>>  Because of this gate the island is a oneway subnetwork (!) and should
>>> get entirely removed in step 2 IMO.
>>>
>>> > On step 3, a very important point are removed due to oneway
>>>
>>>  If just one edge/node is removed there is something wrong. The whole
>>> island should be removed.
>>>
>>> Kind Regards,
>>> Peter
>>>
>>>
>>> On 29.07.2015 09:50, John Zhao wrote:
>>>
>>> Hi Peter,
>>>
>>>  I know the difference between subnetworks and oneway-subnetworks.
>>> I am talking about the step 2 and step 4, not step 3.
>>>
>>>  step 2 and step 4 are both findSubnetwork() with the same parameter.
>>>   minOnewayNetworkSize = 20, minNetworkSize = 200
>>>
>>>  I think I figure out why this discrepancy occurs.
>>> One case is a island in SF bay area. The island has 2 oneway roads
>>> connected to the main network.
>>> http://www.openstreetmap.org/way/53726398
>>>  http://www.openstreetmap.org/way/6374339
>>>
>>>  On step 2, although there is a gate
>>> http://www.openstreetmap.org/node/703042503 on
>>> http://www.openstreetmap.org/way/6374339
>>> And gate block that edge.
>>> The other oneway is connected http://www.openstreetmap.org/way/53726398.
>>> So, this island is connected to the whole network.
>>>
>>>  On step 3, a very important point are removed due to oneway:
>>> http://www.openstreetmap.org/node/678314919
>>>
>>>  Then on step 4, the island are not connected to the main network.
>>>
>>>  *Best Regards,*
>>> *ZhiQiang ZHAO*
>>>
>>> On Tue, Jul 28, 2015 at 11:12 PM, Peter <graphhopper at gmx.de> wrote:
>>>
>>>>  Hi ZhiQiang,
>>>>
>>>> hmmh, not sure if I understand what is unknown at your side.
>>>>
>>>> Subnetworks are different things than oneway-subnetworks. For example
>>>> 4-5 is a oneway subnetwork if connect with a oneway to the main graph only:
>>>> mainGraph->4-5
>>>>
>>>> And this cannot be detected in step 2.
>>>>
>>>> Please have a look at the unit tests to see more examples for the
>>>> different scenes
>>>>
>>>> Regards,
>>>> Peter
>>>>
>>>>
>>>> On 28.07.2015 20:05, John Zhao wrote:
>>>>
>>>> Hi Peter,
>>>>
>>>>  the result I posted is not the result of oneway-subnetwork procedure.
>>>>
>>>>  The total procedures include:
>>>> 1. remove zero-degree node
>>>> 2. findSubnetwork
>>>> 3. oneway-subnetwork procedure
>>>> 4. findSubnetwork again on graphhopper.cleanup()
>>>>
>>>>  My question is, why those islands are recognized on step 4, but not
>>>> on step 2?
>>>>
>>>>
>>>>
>>>>  *Best Regards,*
>>>> *ZhiQiang ZHAO*
>>>>
>>>> On Tue, Jul 28, 2015 at 12:02 AM, Peter <graphhopper at gmx.de> wrote:
>>>>
>>>>>  Hi ZhiQiang,
>>>>>
>>>>> I think it is because both networks are oneway subnetworks not found
>>>>> by the normal subnetwork procedure (but by the oneway-subnetwork procedure)
>>>>> and you defined the oneway minimum size to 20
>>>>>
>>>>> Regards,
>>>>> Peter
>>>>>
>>>>>
>>>>> On 28.07.2015 03:13, John Zhao wrote:
>>>>>
>>>>> Hi Peter,
>>>>>
>>>>>  What I do is:
>>>>> 1. minOnewayNetworkSize = 20, minNetworkSize = 200
>>>>> 2. build san francisco bay area osm data
>>>>> 3. I print out the subnetworks result of the second call.
>>>>>
>>>>> int remainingSubnetworks = preparation.findSubnetworks().size();
>>>>>
>>>>> 4. I found the subnetwork has some smaller than 200, like:
>>>>>
>>>>> subnetwork start from: 37.32611992939085,-121.9961998312816 size: 24
>>>>>
>>>>> subnetwork start from: 37.78373608999855,-122.25065187925067 size: 34
>>>>>
>>>>>  5. I can't understand why the subnetworks with 24 nodes and 34 nodes are not removed by preparation.doWork();
>>>>>
>>>>> It call the same method:
>>>>>
>>>>> Map map = this.findSubnetworks();
>>>>>
>>>>>
>>>>>  *Best Regards,*
>>>>> *ZhiQiang ZHAO*
>>>>>
>>>>> On Mon, Jul 27, 2015 at 12:54 PM, Peter <graphhopper at gmx.de> wrote:
>>>>>
>>>>>>  Hi John,
>>>>>>
>>>>>> sorry, I do not understand your problem or question here. Would you
>>>>>> describe it again step by step for me :) ?
>>>>>>
>>>>>> Kind Regards,
>>>>>> Peter
>>>>>>
>>>>>>
>>>>>> On 27.07.2015 21:45, John Zhao wrote:
>>>>>>
>>>>>> Hi Peter,
>>>>>>
>>>>>>  Thanks.
>>>>>> Actually I only have 1 flagEncoder in the EncodingManager.
>>>>>> The call is exact same, preparation.findSubnetworks()
>>>>>>
>>>>>> preparation.findSubnetworks() using edgeFilter which is also from singleEncoder.
>>>>>>
>>>>>>
>>>>>>  *Best Regards,*
>>>>>> *ZhiQiang ZHAO*
>>>>>>
>>>>>> On Sun, Jul 26, 2015 at 7:56 AM, Peter <graphhopper at gmx.de> wrote:
>>>>>>
>>>>>>>  Hi John,
>>>>>>>
>>>>>>> it should not be related to calling these method twice. It is just
>>>>>>> one time where you calculate the subnetworks independent of any FlagEncoder
>>>>>>> or direction via findSubnetworks and the second pass is FlagEncoder- and
>>>>>>> access-dependent via removeDeadEndUnvisitedNetworks.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Peter
>>>>>>>
>>>>>>>
>>>>>>> On 24.07.2015 21:16, John Zhao wrote:
>>>>>>>
>>>>>>> Hi Peter,
>>>>>>>
>>>>>>>  I am still confused.
>>>>>>> at first we call
>>>>>>> map = findSubnetworks();
>>>>>>>
>>>>>>>  after the cleanup, we call the same method in Graphhopper.
>>>>>>>
>>>>>>> int remainingSubnetworks = preparation.findSubnetworks().size();
>>>>>>>
>>>>>>> Why the subnetwork was recognized the latter time, but not the first time?
>>>>>>>
>>>>>>> we remove some edges make it not connected?
>>>>>>>
>>>>>>>
>>>>>>>  *Best Regards,*
>>>>>>> *ZhiQiang ZHAO*
>>>>>>>
>>>>>>> On Thu, Jul 23, 2015 at 2:22 PM, Peter <graphhopper at gmx.de> wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>  Hi ZhiQiang,
>>>>>>>>
>>>>>>>> yes, according to the wiki this is wrongly mapped:
>>>>>>>> * Avoid tagging highway intersections as that does not make clear
>>>>>>>> which way has the impediment. *
>>>>>>>>
>>>>>>>> http://wiki.openstreetmap.org/wiki/Tag:barrier%3Dgate
>>>>>>>>
>>>>>>>> Peter
>>>>>>>>
>>>>>>>>
>>>>>>>> On 23.07.2015 23:16, John Zhao wrote:
>>>>>>>>
>>>>>>>> Hi Peter,
>>>>>>>>
>>>>>>>>  Maybe the following one related with
>>>>>>>> https://github.com/graphhopper/graphhopper/issues/388#issuecomment-88066385
>>>>>>>>
>>>>>>>>
>>>>>>>>  I have a look at 37.32611992939085,-121.9961998312816.
>>>>>>>> It seesm related with barrier=gate at intersection.
>>>>>>>> http://www.openstreetmap.org/node/1126492194
>>>>>>>>
>>>>>>>>  *Best Regards,*
>>>>>>>> *ZhiQiang ZHAO*
>>>>>>>>
>>>>>>>> On Thu, Jul 23, 2015 at 2:11 PM, Peter <graphhopper at gmx.de> wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>>  There are two types of subnetworks and the smaller ones seems to
>>>>>>>>> be 'one-way subnetworks' which means they are eg. only reachable as
>>>>>>>>> destination or start. But if you would start from a destination-only
>>>>>>>>> subnetwork you'll get 'not found' for all points outside of this network.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Peter
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 23.07.2015 23:03, John Zhao wrote:
>>>>>>>>>
>>>>>>>>>  Interesting,
>>>>>>>>> when I increase minOnewayNetworkSize from 20 to 50, the following
>>>>>>>>> two disappeared.
>>>>>>>>>  subnetwork start from: 37.32611992939085,-121.9961998312816
>>>>>>>>> size: 24
>>>>>>>>> subnetwork start from: 37.78373608999855,-122.25065187925067
>>>>>>>>> size: 34
>>>>>>>>>
>>>>>>>>>  *Best Regards,*
>>>>>>>>> *ZhiQiang ZHAO*
>>>>>>>>>
>>>>>>>>> On Thu, Jul 23, 2015 at 1:55 PM, John Zhao <johnthu at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>>  I tried car flag encoder with following parameter on San
>>>>>>>>>> Francisco bay area data from mapzen.
>>>>>>>>>>
>>>>>>>>>> https://s3.amazonaws.com/metro-extracts.mapzen.com/san-francisco-bay_california.osm.pbf
>>>>>>>>>>
>>>>>>>>>>  minNetworkSize=200
>>>>>>>>>> minOnewayNetworkSize=20
>>>>>>>>>>
>>>>>>>>>>  I printed all the remaining subnetworks.
>>>>>>>>>>  edges: 591932, nodes 437420, there were 3496 subnetworks.
>>>>>>>>>> removed them => 13121 less nodes. Remaining subnetworks:5
>>>>>>>>>> The remaining subnetworks are:
>>>>>>>>>> subnetwork start from: 37.32611992939085,-121.9961998312816 size:
>>>>>>>>>> 24
>>>>>>>>>> subnetwork start from: 37.56018439442332,-122.30257814308803
>>>>>>>>>> size: 436637
>>>>>>>>>> subnetwork start from: 37.78373608999855,-122.25065187925067
>>>>>>>>>> size: 34
>>>>>>>>>> subnetwork start from: 38.180185962770565,-121.70631393878864
>>>>>>>>>> size: 301
>>>>>>>>>> subnetwork start from: 37.85717050411933,-122.07633641532816
>>>>>>>>>> size: 424
>>>>>>>>>>
>>>>>>>>>>  I don't understand why there is still subnetwork less than 200
>>>>>>>>>> nodes.
>>>>>>>>>>
>>>>>>>>>>  I have a look at 37.32611992939085,-121.9961998312816.
>>>>>>>>>> It seesm related with barrier=gate at intersection.
>>>>>>>>>> http://www.openstreetmap.org/node/1126492194
>>>>>>>>>>
>>>>>>>>>>   *Best Regards,*
>>>>>>>>>> *ZhiQiang ZHAO*
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>>>
>>
>
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