[postgis-users] Pgrouting directions

Ahmad Bdair bdair2002 at gmail.com
Mon Jan 5 03:02:28 PST 2009

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

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:

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.


On Wed, Dec 31, 2008 at 7:45 AM, Stephen Woodbridge <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>> 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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