[postgis-users] Create new lines from GPS points

[Stephen Woodbridge]

I think this problem has some hidden assumptions about what is the rate 
of the incoming points, or more appropriately how close together the GPS 
points are and with mis-alignment of GPS with respect to high density 
road networks. If the GPS sample rate is high and the relative distance 
is small percentage of the road network segments then the problem is 
easier to solve because you can assume that any given point is likely on 
the same segment as the last point or just transitioned to the next 
segment in the network.

There are still serious issue if there is a mis-alignment between the 
GPS data and the road segments, especially in dense road network areas. 
Here you might need to apply a stickiness to the segment you are one and 
do additional analysis and in fact defer judgment to N-1 when looking at 
point N.

Also as your sample rate spreads out and the distance between GPS point 
increases then the last segment and the current segment might not even 
be touching so you might need to route between the adjacent GPS points. 
Add to this mis-alignment issues and you have a very tricky problem to 
solve.

The above issues are particularly prevalent in CDMA cell phone tower 
assisted GPS systems that can have a lot of error in urban areas which 
also have higher density road networks, but need to be considered with 
any system like this.

-Steve W

On 1/11/2011 12:15 PM, Ralf Suhr wrote:
> This will work. The GPS point is never on the road geometry.
>
> ST_Line_Substring( road,
>
> ST_Line_Locate_Point(road, ST_ClosestPoint(gps_start, road)),
>
> ST_Line_Locate_Point(road, ST_ClosestPoint(gps_end, road))
>
> ) AS highlight
>
> Gr
>
> Ralf
>
> Am Dienstag 11 Januar 2011, 18:08:29 schrieb Ralf Suhr:
>
>  > Hi Martin.
>
>  >
>
>  > ST_Line_Substring(road, ST_Line_Locate_Point(road, gps_start),
>
>  > ST_Line_Locate_Point(road, gps_end)) AS highlight
>
>  >
>
>  > Gr
>
>  > Ralf
>
>  >
>
>  > Am Dienstag 11 Januar 2011, 17:46:06 schrieb Martin Fafard:
>
>  > > Ralf
>
>  > >
>
>  > > Yes, ok for the buffer. But how to "dynamically segment" my new road
>
>  > > from my original segment?
>
>  > >
>
>  > > Martin
>
>  > >
>
>  > > Ralf Suhr a écrit :
>
>  > > > Hi Martin,
>
>  > > >
>
>  > > > you will not get a correct solution for this problem. Your road
> network
>
>  > > > and the gps points differs always.
>
>  > > >
>
>  > > > A possible "solution" is building a buffer around the streets und
> look
>
>  > > > für intersection with gps points and filter by direction road/points.
>
>  > > > Grouping gps points can give you the start and end point for the
> road.
>
>  > > > If a road is only one times driven.
>
>  > > >
>
>  > > > Gr
>
>  > > > Ralf
>
>  > > >
>
>  > > > Am Dienstag 11 Januar 2011, 17:16:18 schrieb Martin Fafard:
>
>  > > >> Hi
>
>  > > >>
>
>  > > >> I have a network of roads (topological) and I receive GPS points. I
>
>  > > >> would like to create new lines who follow exactly the same path
> as my
>
>  > > >> road from the GPS points (to "highlight" where the GPS unit was
> on the
>
>  > > >> network). The problem is I need to segment the new line because the
>
>  > > >> GPS points can stop anywhere on my roads... Any advice to do this?
>
>  > > >> Thank you
>
>  > > >>
>
>  > > >> Martin F
>
>  > > >> _______________________________________________
>
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>
>  > > >> postgis-users at postgis.refractions.net
>
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>
>
>
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