[GraphHopper] There must be bug on the subnetwork removal

John Zhao johnthu at gmail.com
Wed Jul 29 09:18:57 UTC 2015 

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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>>>
>>
>>
>>
>
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