[pgrouting-dev] Gsoc 2013 Preliminary project proposal

[Stephen Woodbridge]

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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