[postgis-users] match line with road segment

[searchelite]

searchelite wrote:
> 
> 
> 
> Obe, Regina     DND\MIS wrote:
>> 
>> Now you do your make line.  But you'll have to take into consideration
>> what Paolo Rizzi said afterward.  Not sure the easiest way to do that.
>>  
>> So basically your process should look something like the below where
>> trip_id is some fied that uniquely identifies each trip.  The below snaps
>> each point to closest road segment and then makes a line for each trip. 
>> It assumes the pt.gid is in the order of time travel.  If you have a
>> datetime field for each point, use that instead of the pt.gid.
>>  
>>  SELECT trip_id, ST_MakeLine(snapped_point) As trip_route
>> (SELECT
>> pt_id,
>> ln_id,
>> 
>> ST_Line_Interpolate_Point(
>>  ln_geom,
>>  ST_Line_Locate_Point(ln_geom, pt_geom)
>>  ) As snapped_point,
>> travel_id
>> 
>> FROM
>> (
>> SELECT DISTINCT ON (pt.gid)
>>  ln.the_geom AS ln_geom,
>>  pt.the_geom AS pt_geom,
>>  ln.id AS ln_id,
>>  pt.gid AS pt_id,pt.trip_id
>> FROM
>> gps_points pt INNER JOIN
>> road_table ln
>> ON
>> ST_DWithin(pt.the_geom, ln.the_geom, 10.0)
>> ORDER BY
>> pt.gid,ST_Distance(ln.the_geom, pt.the_geom)
>> ) AS subquery ORDER BY trip_id, pt_id) As snapped_points
>> GROUP BY travel_id;
>>  
>> Hope that helps,
>> Regina
>> 
>> 
> 
> 
> thanks a lot for the reply...i'll try the code you give me first thing
> tomorrow...:-)
> 
> 

basically, the code you gave me just create a line from snapped points
right? what about matching the route with the road? I want to make the route
like the illustration below

http://www.nabble.com/file/p18522213/untitled.jpg 


thank you



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