[postgis-users] How to check if two linestring are near to each other

[Åsmund Tokheim]

Hi

The test
select st_hausdorffdistance(st_geometryfromtext('LineString(0 0, 1 0)'),
st_geometryfromtext('LineString(0 5, 1 5)'))
gives a distance of 5, not 0 as one would expect if HD only measured shape
similarity, so I think it still can be used for your task. Something like
hibernate spatial should provide programmatic interfaces for common gis
functions, but I suspect you have to write native sql if you want to use
postgis-specific functions like hausdorffdistance.

Åsmund


On Mon, Apr 14, 2014 at 9:36 AM, Rémi Cura <remi.cura at gmail.com> wrote:

> Hey,
> I'm not so sure Hausdorff distance is what you want.
> It measure how similar 2 shapes are, yet you could have two very similar
> parts of a road network that are very far away.
> In you case you are trying to express both lines that are close to each
> other __and__ that are similar in shape.
>
> Of course the obvious (but painfull) way to go would be to use postgis
> topology with the tolerance set to your GPS error (+ width of the road).
> This way close path would be merged automatically.
>
> Cheers,
> Rémi-C
>
>
> 2014-04-13 23:56 GMT+02:00 Raghavan Krishnasamylakshmanaperumal <
> rkrish20 at uic.edu>:
>
> Hi Åsmund,
>>
>> Thanks for suggesting ST_HausdorffDistance, I tried this function
>> directly on the database using sql query and it looks like solving my
>> problem.
>>
>> Are these functions ST_HausdorffDistance/ST_Distance available as java
>> APIs? I am trying to use org.postgis(postgis-jdbc-1.3.1.jar) library but
>> not sure how to access the above mentioned functions using java. Please
>> suggest me which package to look into to make use of these functions
>> programmatically?
>>
>> Thanks in advance.
>>
>> -Raghavan
>>
>>
>> On Sun, Apr 13, 2014 at 1:45 PM, Åsmund Tokheim <asmundto at gmail.com>wrote:
>>
>>> Hi
>>>
>>> I think you should be able to use hausdorff distance
>>> http://postgis.net/docs/ST_HausdorffDistance.html to recognize that the
>>> green, red and blue lines in your image are all similar. This method will
>>> fail to recognize shared portions of a path (e.g. if the blue line at some
>>> point diverges from the red and green line), but I'm not sure if this is a
>>> requirement for your task
>>>
>>> Åsmund
>>>
>>>
>>> On Sat, Apr 12, 2014 at 9:41 PM, Raghavan Krishnasamylakshmanaperumal <
>>> rkrish20 at uic.edu> wrote:
>>>
>>>> Hi,
>>>>
>>>> I have formed a graph using my GPS traces of running/biking activities
>>>> in which I have many edges representing the same path. For example every
>>>> time I run from node-A to node-B my GPS traces are noted close to each
>>>> other like the red,green,blue lines in the attached image. Actually those 3
>>>> lines are same(representing the same path), so I want to detect such
>>>> linestrings automatically and keep only one linestring and ignore others.
>>>> Is there any way in PostGIS which can help me to detect the
>>>> nearness/closeness of the linestrings?
>>>>
>>>> --
>>>> Thanks and Regards,
>>>> Raghavan KL
>>>>
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>>>>
>>>
>>>
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>>
>>
>>
>> --
>> Thanks and Regards,
>> Raghavan KL
>>
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