[postgis-users] Using routing to create polygons of estimated travel distances

Stephen Woodbridge woodbri at swoodbridge.com
Thu Apr 30 22:12:01 PDT 2009

Simon O'Malley wrote:
> Hi List
> Trying to get my head around the easiest way to generate a contour map 
> of travel times from a central location based on road centreline network.
> We have a central location and need to generate polygons showing which 
> properties are with 5, 10, 15 etc minutes of this location.
> A road network is present with estimated speeds along each segment so we 
> can calculate estimated travel time along each segment.
> How do we go about traversing the networking and creating points at say 
> 5 minute intervals, making sure we are travelling away from the central 
> location.
> The idea was then to join up the points to create polygons and overlay 
> over the property boundaries.
> Any ideas/help much appreciated.

Hi Simon,

Have you looks at pgRouting? It does the drivetime analysis. Once you 
have the cost to get to each node in the network, you can use the cost 
as a Z value of each XY of each node in the graph. You can then use 
these XYZ points to build a triangluar surface in 3D where Z represents 
the time. If you slice the triangles based on constant Z-levels you will 
get the edges of the polygon. But all of this requires a lot of post 
processing of the pgRouting results.

You might be able to do the whole thing, routing, and isochronal 
polygons in Grass.


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