[postgis-users] Transportation representation of a postgis linear layer

[ahmed at elegantdesigns.ca]

Steven,

I'm trying to do some network assignment on my road layer. I already know
the trips genereated and produced between zones and the different modes
they have to use. Right now i want to assign these volumes to road links.
this is a simplistic model of the procedur:
http://en.wikipedia.org/wiki/Route_assignment .
The road layer provided does not contain any of the turning movememnt
restrictions or proper ramp and ineterchange representations. 

So my first task is to re-represent the layer into something i can do some
calculations with and
Second i can apply the proper algorithms to my table to generate my results

cheers,
Ahmed


Ahmed
ahmed at elegantdesigns.ca wrote:
> Hey List,
> 
> I have a road centerline layer for a local municipality, I was wondering:
> 
> * how can I conver the intersections similar to what's found on
>
ftp://ftp.cits.rncan.gc.ca/pub/information/NRN_V2/Geobase_Best_Practices_NRN.pdf
> page 11 and 12 section 3.2.3?
> 
> * What are some of the ways I can represent road directionality? 

create a oneway column and use values like:

TF  traffic flow is one way to_node -> from_node
FT  traffic flow is one way from_node -> to_node
B | blank | null  taffic flow is both ways

> * How can I represent center-turning lanes (usually a lane between lanes
> where people can turn left)

1) tag the segment with the number of lanes and add attributes which 
identify restrictions by lane number
2) digitize multiple lanes and apply turn restrictions as appropriate.

> * what are some of the ways to represent a non-interchange
> overpass/underpass?

This depends on whether you model needs to be fully noded at all virtual 
intersections or not. If not then you can just digitize them so thay to 
not intersect at a common node. It is more common, to fully node all 
intersections and then set a z-level attribute for each end. So at 
ground level the segments would have a z-level=0 and at one level of 
overpass the z-level=1, etc. so a ramp from ground level up to an over 
pass might have z-levels on 0 and 1 at its respective ends.

I think the bigger question is assuming you have all this data entered, 
what to you plan to do with it? I assume load it into a router, but then 
the question becomes what are the requirements of the router and what 
are the requires for entering z-levels, and turn restrictions.

-Steve W

> cheers,
> dassouki
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