[pgrouting-dev] Gsoc 2013 Preliminary project proposal
Mukul priya
mukul2047 at gmail.com
Thu Apr 11 12:24:02 PDT 2013
Hi Steve and Daniel,
You suggested extending the present algorithms such that its input
can take more points and not only the source and destination . i think this
can be implemented and i will soon come up with implementation details(
kind of more technical ) .
Can you be a liitle bit more elaborate about partioning data into
spatial chunks or even suggest some readings . I can then come up with some
better ideas about implementing it.
Daniel , i took a look at the oracle link that you provided but
there was no details about how it has been implemented , it was more about
how one can use it. May be a bit more search and luck might take me to
its implementation document :) .
The other thing that you mentioned was about contraction Hierarchy
. Still the nodes have to be ordered based on some criteria or according to
their importance . We can use natural hierarchy present in the network for
doing that .
i will be really grateful if anyone can correct me in case if my
thought process in not on the right lane and sorry for the late reply as my
academic session is in progress too .Meanwhile i am trying to get fluent
with git ,cmake and other tools.
Thanks .
Mukul
On Thu, Apr 11, 2013 at 6:47 PM, Stephen Woodbridge <woodbri at swoodbridge.com
> wrote:
> With pgRouting, we do most things dynamically, here is the basic flow:
>
> 1. Given a collection of input, points, nodes, or edges
> map these to nodes or edges depending on algorithm.
>
> 2. Select the edges we need to build the graph
>
> 3. build the graph and solve it
>
> 4. return the results
>
> All our algorithms today only take start and end points. They could be
> extended to take points. Each "point" (I use "point" as a generic term
> because it might be a lat/lon, node id, edge id and offset, etc) would need
> to be mapped to the appropriate input need for any given algorithm.
>
> So for node based algorithms like Dijkstra,and astar it would get resolved
> to a node. For TRSP it would get mapped to the nearest edge and offset
> along that edge. Postgis has lots of handy tools for doing this.
>
> -Steve
>
>
> On 4/10/2013 10:50 PM, Mukul priya wrote:
>
>> Thanks for the reply steve . i have already cloned the github repository
>> and looking into various aspects of it .
>>
>> For IRNN querry implementation i think it is a good idea to sub divide
>> the whole route and generate n+1 routes separately , say from S to F1 ,
>> F1-F2 ,..... F(n-1)-Fn , Fn to D . i wanted to know if we have that kind
>> of a data where each and every facility is mentioned on the map as a
>> point (node ) . even if it is not directly connected to the road network
>> we can basically treat it a pseudo node and then call the router . The
>> other thing about optimization yes we can do that using spatial range
>> querries suppose there are several instances of the same facility that a
>> user wants to access then we can use spatial range querries to locate
>> that facility which is the nearest.
>>
>>
>> On Thu, Apr 11, 2013 at 1:42 AM, Stephen Woodbridge
>> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.**com<woodbri at swoodbridge.com>>>
>> wrote:
>>
>> On 4/10/2013 3:23 PM, Mukul priya wrote:
>>
>>
>> Hi ,
>>
>>
>> Hi Mukul,
>>
>> Thank you for your interest in pgRouting.
>>
>> I am a B.tech fourth year student at
>> IIIT-Hyderabad
>> pursuing a degree in computer science and engineering and i will
>> be soon
>> pursuing a Masters Degree in the field of Spatial Informatics
>> and the
>> research topic that i have been working on is *"In route nearest
>> neighbour querries".*
>>
>>
>> Last year i worked on a project that was funded by
>> Honeywell technology solutions and it gave me a lot of insight
>> about
>> open source programming and industrial work culture.
>>
>> I was introduced to pgrouting by *Prof. Venkatesh Raghavan* who
>> visited
>>
>> our college last summer. i have also used pgrouting for
>> implementing one
>> of my Honors project.
>>
>> i have gone through the updated ideas page and i am listing out
>> a topic
>> that i feel i can contribute to.
>>
>> *Idea *
>>
>> Network Partitioning
>>
>> A very simple method using which it can be done is :
>>
>> * *Existence of a natural Hierarchy*
>>
>>
>> Generally road networks are organized such that there
>> is some
>> natural hierarchy for example if we look at the road network of
>> USA we
>> observe that there are national highways which connect multiple
>> large
>> regions , inter state roads connect places within these regions
>> , multi
>> lane roads connect city areas and then there are small roads to
>> connect
>> individual houses.
>>
>> so what we can do is first rank these classes that
>> constitute the road network and then use the highest level roads
>> to
>> divide the road network into large regions enclosed by these
>> roads. each
>> of the divided regions can further be divided again using next
>> lower
>> level road.
>>
>> so suppose we have a road network which n classes of
>> different roads then we can create a tree of depth n-1 where the
>> root of
>> the tree will represent the entire road network and children of
>> the the
>> root node will represent the area formed by partitioning the
>> root using
>> the level 1 ( highest ) edges and so on . the nodes will basically
>> represent a smaller part of the road network.
>>
>> The idea seems to be very naive right now but if
>> anyone can
>> give some feedback whether it is achievable or not or may be
>> suggest
>> some modifications.
>>
>>
>> Yes this is the basics of how this could work. Because we build our
>> graphs dynamically for each route request, we can do something like
>> this today. Typically you have to feed the route request and SQL
>> query that provides the edges needed to build the graph and this can
>> be simply the bounding box of the start and end point of the route
>> expanded slightly to allow the route move outside that bounds by a
>> little if needed. A case in point are start and end points that form
>> a vertical of horizontal line.
>>
>> So for the natural hierarchy, you can for a SQL query like:
>>
>> select * from edges where st_dwithin(the_geom, start_pnt, radius)
>> union
>> select * from edges where st_dwithin(the_geom, end_pnt, radius)
>> union
>> select * from edges
>> where st_expand(st_makeline(start___**pnt, end_pnt), pct)
>>
>> and road_class < 4;
>>
>> So this gets all edges regardless of class at the start and end and
>> then gets all the major roads and highways between the start and end
>> points. We can dynamically select the edges that we want when we
>> build the graph.
>>
>> Regardless of how you implement the routing, the problem is all
>> about the data. If you have a road segment the is misqualified, you
>> might end up with a network that is broken between start and end.
>> This can alsoo happen if ramps are not coded correctly.
>>
>> One of the challenges we have today is that we have to be able to
>> construct the whole graph in memory before we can start routing.
>> This is ok for small areas but it is a problem if you want to
>> generate a route between say Miami, Florida and Seattle, Washington.
>> An interesting problem would be the ability to partition the data in
>> spatial chucks and only load them as the solver needed them.
>>
>> If you think about your edges sorted into say 1 degree grid
>> partitions,
>> then you load the partition for the start point and start routing
>> using A* search, when you frontier get to an edge of the grid you
>> are in, then you load the adjacent grid and continue, if you bump
>> into another grid boundary that is not loaded yet, you load, if it
>> is already loaded you continue. Anyway food for thought! :)
>>
>>
>> In route nearest neighbour querries( IRNN) which
>> handle
>> querries like computation of shortest path , provided that the
>> user
>> wants to visit facilities F1 , F2 ,.....FN while he/she drives
>> or walks
>> from source to destination. Network partitioning can optimize
>> these
>> computations too as the search space reduces significantly once
>> we have
>> the partitions. Handling such querries have not been implemented
>> yet. It
>> will be very helpful if we can have some discussion about whether
>> implementing it is feasible or not.
>>
>>
>> What is we just added via support to routing? Then we could do
>> something like say generate a route: Start, F1, F2, ... Fn, End
>> This would allow us to build a graph one time and then generate
>> multiple sub-routes with in the graph. Today if you want to do that
>> you have to generate n+1 routes and build the graph n+1 times. We
>> could also do some preliminary optimization of the via points based
>> on Euclidean distance using something like TSP before calling the
>> router.
>>
>>
>>
>> It would be great if someone could give a general
>> idea
>> how to go about learning more about the areas mentioned with
>> respect
>> to the organization's projects.Specially suggest those ideas
>> which the
>> developers think are achievable for now . I will also be grateful
>> if
>> somebody can guide me regarding the development framework of
>> pgrouting
>> so that i get familiar with the whole framework in the coming
>> days.
>>
>>
>> I would clone the github repository and look at branch sew-devel-2_0
>> this is our new tree structure and it has code, doc, and test all
>> organized in a nice way that makes it easy to multiple contributors
>> work with the tree.
>>
>> Ask questions, There is a tutorial floating around and lots of
>> people that are will to help.
>>
>> -Steve
>>
>> Thank you .
>>
>> Mukul Priya
>> Lab for spatial Informatics
>> IIIT-Hyderabad
>>
>>
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