[pgrouting-users] pgrouting - Cleber Arruda from Sweden - driving direction.

[Cleber Arruda]

Hey Stephen,
Pretty fast
Thank you.

I will implement what you suggested and let see what I will come up with.

Once more thanks.
It was a nice talk with you on the phone.

Take care...

On Tue, Jan 25, 2011 at 2:40 AM, Stephen Woodbridge <woodbri at swoodbridge.com
> wrote:

>  On 1/24/2011 5:44 PM, Cleber Arruda wrote:
>
> Hello,
> Hi Stephen how are you? I hope you are fine and enjoying life.
> Well, I am doing my master thesis in Sweden in Geomatics as I mentioned to
> you on the phone.
> My Master thesis topic is the development of routing network using
> pgrouting and OSM.
> So, I have been looking for the solution for this problem since October
> 2010. I have stopped the written part of my thesis and started the technical
> part. I have to finish write the application - the routing using pgrouting -
> just the one you have on
> http://gis.imaptools.com/routing/leaddog/?zoom=10&lat=33.85667&lon=35.52978&layers=B0TTTF&start=35.492313%2033.826188&stop=35.595811%2033.906827&method=STS&lang=eng
> ).
>
> I would appreciate if you can guide me through the steps to find the best
> route and draw the segment/path correctly from the start point to the end
> point.
> Well, I am sending you a print screen of what I have got so far.
>
>  Hi Cléber,
>
> So the process for dealing with the segments is as follows.
>
> 1. we assume that the list of segments is in the correct order from start
> to end of the route, but any given segment might be flipped backwards. For
> example the segment is loaded as A->B but in the graph we traverse it from
> B->A. We will always get the segment in the result as A->B. So this is the
> process to flip the segments. For this pseudo-code I will use the following
> notation:
>
> S[n]  - segment n
> S[n].A  - is the point at the start of the segment
> S[n].B  - is the point at the end of the segment
>
> A. check if we need to flip the first segment, If the start of the 1st
> segment is connected to the 2nd segment we need to flip it:
>
> if (S[0].A == S[1].A or S[0].A == S[1].B) then reverse(S[0]);
>
> See:
> http://postgis.refractions.net/docs/index.html     -- main postgis
> reference manual
> http://www.postgresql.org/docs/                           -- main
> postgresql docs
> You might want to look for plpgsql language examples
>
> http://postgis.refractions.net/docs/ST_Reverse.html
> http://postgis.refractions.net/docs/ST_Distance.html
> http://postgis.refractions.net/docs/ST_StartPoint.html
> http://postgis.refractions.net/docs/ST_EndPoint.html
>
> You can translate S[0].A == S[1].A into something like:
>
> distance(st_startpoint(seg0), st_startpoint(seg1)) < tolerance
>
>
> B. now we need to check the rest of the segments assuming S[0]
>
> for (i=1; i<count(S); i++) {
>     if(S[i-1].B == S[i].B) then reverse(S[i]);
> }
>
> 2. now all the segments are order correctly from start to finish. There are
> some corner cases that you need to check for and deal with, like the start
> and end are on the same segment and there is only one segment in the result.
> You might need to check for gaps between the segments, but if the data was
> prepared correctly you should not need to worry about this. Now we need to
> trim the first and last segments. Look at the postGIS linear referencing
> functions for the tools to do this.
>
> A. first we trim the start, we assume "start" is the start point for the
> route. We have already flipped it if that was needed. We can think of the
> problem like this:
>
> A----------P-----------B
>
> where A->B is S[0] and P is our "start point. We know that  the 2nd segment
> is connected to B so we want P->B:
>
> S[0] = *ST_Line_Substring*(S[0], *ST_Line_Locate_Point*(S[0], start),
> 1.0);
>
> http://postgis.refractions.net/docs/ST_Line_Substring.html
> http://postgis.refractions.net/docs/ST_Line_Locate_Point.html
>
> B. likewise we need to trim the last segment, it has also been flipped if
> needed. And this problem is:
>
> A---------P------------B
>
> Where A->B is the last segment and the n-1 segment is connect to A so we
> want A->P in this case:
>
> S[n] = *ST_Line_Substring*(S[n], 0.0, *ST_Line_Locate_Point*(S[n], end));
>
> So this is the basic algorithm. You can see it is fairly simple and
> straight forward. The trick is converting this into plpgsql language. You
> typically do not work with arrays in plpgsql, but with record sets and set
> returning function. A lot of people that are more familiar with PHP, get the
> results back in PHP and post process the data there.
>
> See what you can do with this. I'm also going to post this to the pgRouting
> list so other can help and learn for this. If you are not subscribed to the
> list you should be as there are lots of people there that can help if I'm
> not available.
>
> Thanks for your call today and best regards,
>   -Steve
>    http://imaptools.com/
>
> Thanks and take care.
> I hope that together we strive to achieve excellence for a better world in
> this wonderful field and for all newcomer generations.
>
> --
> Cléber D. Arruda
> Kämnärsvägen 33C
> 226 46
> Lund - Sweden
> Phone +46737762526
> E-mail: cleverdo at gmail.com
>
> Peace and Love Always.
>
>
>


-- 
Cléber D. Arruda
Kämnärsvägen 33C
226 46
Lund - Sweden
Phone +46737762526
E-mail: cleverdo at gmail.com

Peace and Love Always.
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