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

[Simon O'Malley]

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.

 

Simon

[Stephen Woodbridge]

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.

-Steve
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[Anton Patrushev]

Hi Simon,

You can try to use Driving Distance function of pgRouting
(http://pgrouting.postlbs.org/wiki/DrivingDistance) - this is exactly
what you need.

Anton.

[Anton Patrushev]

Hi Steve,

Yes, you can process the result of core Driving Distance function with
Convex Hull function of PostGIS or with point_as_polygon function of
pgRouting, but there is a wrapper around this core function already
which returns you a polygon
(http://pgrouting.postlbs.org/browser/trunk/extra/driving_distance/sql/routing_dd_wrappers.sql#L78)
right away.

Anton.