[postgis-users] Pgrouting directions
a7mad
bdair2002 at gmail.com
Mon Jan 5 12:07:21 PST 2009
Stephen Woodbridge wrote:
> In the example I used below, the road segment would have had 4 points,
> but regardless of the number of points, you would use:
>
> pnt[1], pnt[2] for the calculations at the start of the segment.
> pnt[numpoints-1], pnt[numpoints] for the calculations at the end of
> the segment.
>
> So in postgis you could use:
>
> st_x(st_pointn(the_geom, 1)) or st_x(st_startpoint(the_geom))
> st_y(st_pointn(the_geom, 1)) or st_y(st_startpoint(the_geom))
>
> st_x(st_pointn(the_geom, 2))
> st_y(st_pointn(the_geom, 2))
>
> st_x(st_pointn(the_geom, st_numpoints(the_geom)-1))
> st_y(st_pointn(the_geom, st_numpoints(the_geom)-1))
>
> st_x(st_pointn(the_geom, st_numpoints(the_geom))) or
> st_x(st_endpoint(the_geom))
> st_y(st_pointn(the_geom, st_numpoints(the_geom))) or
> st_y(st_endpoint(the_geom))
>
>
> If you need to compute the bearing or Azimuth of the segment ends look
> at this:
> http://postgis.refractions.net/pipermail/postgis-users/2007-November/017768.html
>
> http://postgis.refractions.net/documentation/manual-svn/ST_Azimuth.html
>
> -Steve
>
> Ahmad Bdair wrote:
>> Thanx Steve, your information were helpful, but when I think of it it
>> confuses me a lot, lets first start with my fields in DB.
>>
>> Columns are:
>> gid serial NOT NULL,
>> rod_name_a character varying(50),
>> label character varying(50),
>> rod_length integer,
>> rod_no integer,
>> rod_type character varying(1),
>> rod_class character varying(1),
>> rod_code character varying(10),
>> shape_leng numeric,
>> the_geom geometry,
>> source integer,
>> target integer,
>> length double precision,
>> x1 double precision,
>> y1 double precision,
>> x2 double precision,
>> y2 double precision,
>> to_cost double precision,
>> "rule" text,
>> cost_factor integer,
>> main_cost double precision,
>> reverse_cost double precision,
>> roadclass text DEFAULT 'OTHER'::text,
>> cost_reverse_factor integer DEFAULT 5,
>>
>> Now, I am confused, because I cannot calculate the heading in the
>> first place, If I have
>> B+---\
>> x2,y2
>> |
>> x1,y1
>> A+---/
>>
>> Now I can calculate the heading simply by comparing x1 and y1 to x2
>> to y2 and which is larger (based on lonlat) so I can judge it, but
>> some times I am having this:
>> B+---\
>> x1,y1
>> |
>> x2,y2
>> A+---/
>>
>> Now it is misleading, maybe thats why you told me not to use start
>> and end point, but wait, what else to use ? According to my DB I
>> cannot think of any other way to calculate headings and angles.
>>
>> Regards
>>
>> On Wed, Dec 31, 2008 at 7:45 AM, Stephen Woodbridge
>> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.com>> wrote:
>>
>> Ahmad Bdair wrote:
>>
>> Yes, that is something very similar to what I need to do, I
>> already wrote a php code to check angels and slopes, but it was
>> not accurate, it was more life "if else" code, I check the
>> longlat for current segment
>>
>>
>> When you check the angles do not use the end points because they are
>> mis-leading.
>>
>> B+---\
>> |
>> A+---/
>>
>> If you have a segment from A to B like the above and you calculate
>> the heading or angles based on the vector AB then it will point
>> north and is should be pointing west at the end of the vector or
>> east at the start of the vector.
>>
>> You also need to look at weather or not you need to flip segments
>> because you route might traverse them from start to end OR from end
>> to start.
>>
>> When I compute angles I grid the angles into 8 pie pieces of 45
>> degrees each.
>>
>> continue straight
>> turn slight right/left
>> turn right/left
>> turn sharp right/left
>> make a u-turn
>>
>>
>> with longlat for the previous one, I guess you didn't use the
>> database for direction calculation(except for routing) am I
>> right? Isn't steps 3 and 4 depends on your angel calculations?
>>
>>
>> I have done this in C in a prototype router I wrote years ago. I
>> have implemented it in PHP and in perl in various incarnations in
>> the past. The demo page has it written in pgpsql, but it is based on
>> my own heavily modified versions of the pgRouting stored procedures.
>>
>> Hope the above helps with your problems. I find it easiest to work
>> out the math problems of computing the angles and headings first and
>> make sure they are correct. Then move on to the other issues. If
>> your math is wrong computing the headings and angles it will cloud
>> all the other results.
>>
>> Best regards,
>> -Steve
>>
>> I have the roads with two different languages, a road map like
>> anyother road map I guess.
>>
>> On Tue, Dec 30, 2008 at 3:17 AM, Stephen Woodbridge
>> <woodbri at swoodbridge.com <mailto:woodbri at swoodbridge.com>
>> <mailto:woodbri at swoodbridge.com
>> <mailto:woodbri at swoodbridge.com>>> wrote:
>>
>> bdair2002 wrote:
>>
>> Hello,
>> I am developing an application using Pgrouting with
>> Postgis
>> data, everything
>> is fine, but now I am looking to do something like
>> Google
>> directions guide,
>> where it tells you turn left or right, I am wondering
>> if this
>> feature is a
>> built-in feature in Pgrouting or Postgis.
>>
>> Regards
>>
>>
>> No this is not a feature that is part of either.
>>
>> I have implemented a directions explicator, but it is
>> somewhat
>> specific to the data that you have, as you need to know what
>> column(s) contain the road names, if you have signage
>> information
>> then you need to know how to link to that. If you want to be
>> able to
>> explicate in multiple languages, then you probably need to
>> consider
>> supporting multiple languages each in a separate table the
>> you can
>> select from when you generate the languages.
>>
>> The algorithm is pretty straight forward as the you currently
>> get a
>> list of segments that make up the route. Then you need to:
>>
>> analyze each segment and
>> 1) check to see if you want to join it with the previous
>> segment
>> because the road name matches
>> 2) check the angle that it makes with the last segment to
>> determine
>> right, left, straightness of turn
>> 3) compute the compass heading for the segment
>> 4) determine if you have signage
>> 5) based on these, determine if you are read to explicate and
>> which
>> predefined instruction you need to explicate an instruction
>> 6) loop through all segments
>>
>> For a demo of this you can try:
>> http://imaptools.com/leaddog/routing/dd.html
>>
>> Zoom into a city in one of the yellow areas, set a start
>> and end
>> point and click [calculate route] button. The driving
>> directions
>> should show below the button if it was successful, be
>> patience the
>> routing is running on a 333MHz box.
>>
>> -Steve
>>
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Now that makes a lot of sense, thank you very much, by the way, offtopic
subject, I tried to enable routing to work on IE without any success, I
checked your site but it is not working also (IE 7), is there any work
around for IE (I know it sucks to develop on IE).