[mapserver-users] optimal path between two points.

[Stephen Woodbridge]

Valeria Muñoz wrote:
> Hi Stephen
>  
>  thanks for the tip... I read the example and implements it with my data.
>  
> Now my problem is :how to rescue the data for instructions,distance,time 
> etc? ..
> how can I know whether to turn right or left?

Assume you have two segments a->b and a->c and we want to evaluate it at a

1) you need to check if segment a->b needs to be flipped end to end.

2) because segments can be curves like highway exit ramps you can not 
just use the endpoints, instead you have to use:
ab[npoints], ab[npoints-1] and compute the azimuth of this
ac[1], ac[2] and compute the azimuth of this

3) then based on the change in azimuth you and determine if the route is 
changing directions and turning right or left

See postGIS functions:

ST_NumPoints()
ST_pointN()
Reverse()
Azimuth()

-Steve

> RG.
> 2009/1/20 Stephen Woodbridge <woodbri at swoodbridge.com 
> <mailto:woodbri at swoodbridge.com>>
> 
>     Valeria,
> 
>     You should really look at the example provided with:
>     http://pgrouting.postlbs.org/wiki/WorkshopFOSS4G2007
> 
>     This is what I started with and then made my own modifications. The
>     above workshop should walk you through how to setup a pgRouting
>     without my additional hacks which will only confuse you at the moment.
> 
>     My dd_routing.php is a modified version of ax_routing.php that is
>     included in the tutorial tarball.
> 
>     You might also want to read some of these pages if you have not already:
>     http://www.google.com/search?hl=en&q=pgRouting&btnG=Google+Search
>     <http://www.google.com/search?hl=en&q=pgRouting&btnG=Google+Search>
> 
>     Best regards,
>      -Steve W
> 
>     Valeria Muñoz wrote:
> 
>         hi Stephen.. thank for the tips...
>         I have reviewed the code but can only see the dd.html. can you
>         send me the dd_routing.php? .
>          please
> 
>         thanks for everything
>         2009/1/19 Stephen Woodbridge <woodbri at swoodbridge.com
>         <mailto:woodbri at swoodbridge.com> <mailto:woodbri at swoodbridge.com
>         <mailto:woodbri at swoodbridge.com>>>
> 
> 
>            Valeria Muñoz wrote:
> 
>                frank
>                 thanks for the tips.  I use prRouting  and create the table
>                dijsktra_result. Now how can I implement with my mapfile?
>         , how
>                deliver the data .. have some sample code?
> 
>                thanks for your help.
> 
>                2009/1/19 Frank Warmerdam <warmerdam at pobox.com
>         <mailto:warmerdam at pobox.com>
>                <mailto:warmerdam at pobox.com <mailto:warmerdam at pobox.com>>
>         <mailto:warmerdam at pobox.com <mailto:warmerdam at pobox.com>
> 
>                <mailto:warmerdam at pobox.com <mailto:warmerdam at pobox.com>>>>
> 
> 
>                   Valeria Muñoz wrote:
> 
>                       Hi
>                        I would like to implement the service "optimum path
>                between 2
>                       points," can someone help me to be able to
>         implement it?. The
>                       general idea is that a user picks a point A and
>         point B and a
>                       display on the map the best route to get from
>         point A to B.
> 
> 
>                   Valeria,
> 
>                   MapServer itself does not do route calculation.  You might
>                find some
>                   useful pointers on this page:
> 
>                    http://wiki.osgeo.org/wiki/OpenRouter
> 
>                   I think the pgRouting (built on postgres/postgis) is
>         the best
>                bet for
>                   integration with MapServer.
> 
> 
>            So you have various options depending on the client software
>         you are
>            using. So here are some ideas for you:
> 
>            1) put the route into a results table with a unique id, and
>         pass the
>            unique id back to the client where it can then request the route
>            image via a mapserver mapfile the connects to the postgis
>         database
>            and requests the layer be drawn with the unique id to select the
>            appropriate route.
> 
>            2) make an ajax request to generate the route and return the
>            polyline as  an xml or json object back to the client. The client
>            then parses the result document and displays the route over
>         the map.
> 
>            3) if you use OpenLayers for the client then you can use it
>         to help
>            you do 1) as an image, or 1) as a wfs layer, or 2) as a
>         vector layer.
> 
>            You can look at the source for my demo page
>            http://imaptools.com/leaddog/routing/dd.html which does this
>         with a
>            modified version of pgRouting (pgRouting does not return
>            turn-by-turn directions), but you should be able to modify my
>         code
>            to work with pgRouting. I wrote a simple php script to proxy the
>            route request into postgres and to format the results back to the
>            client.
> 
>            Look this over and see how far you can get with this. If you get
>            stuck, ask and I'm sure we can get you moving in the right
>         direction.
> 
> 
> 
>