Martin,
You just have to break the problem down into smaller tasks like:
1. project the point onto the closest road segment
2. if I have a previous point that I already projected
3. if that point is on the same segment as this point
4. extract the sub-segment from previous point to this point
5. if the two point are not on the same segment
6. see if the two segments are connected by comparing end points
7. if connected, the extract the segment from previous to connected end
and connected end to current point
8. if they are not connected then route from previous point to current
point and then extract those segments
I will leave how to route up to you for now. You can look at pgrouting
or doing BFS of connected segments until you find the segment your
current point is on.
Look in the postgis reference for the linear referencing functions fo
how to project a point onto a segment and how to extract a portion of a
segment.
-Steve
http://imaptools.com/
On 1/13/2011 9:50 AM, Martin Fafard wrote:
Hi
Last step for my problem. Following the attached jpg, I need to
highlight (create new line) the topological road (black) only when it
intersect the green line
Any advice?
Thank you
Martin
Stephen Woodbridge a écrit :
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
> > >> _______________________________________________
> > >> postgis-users mailing list
> > >> [email protected]
> > >> http://postgis.refractions.net/mailman/listinfo/postgis-users
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