[pgrouting-users] Driving distance/pgr_alphaShape/pgr_pointsAsPolygon

Stephen Woodbridge woodbri at swoodbridge.com
Tue Nov 11 10:00:48 PST 2014

On 11/11/2014 3:30 AM, dave.potts at pinan.co.uk wrote:
> Hi list,
> I am trying to work out why I would want to use pgr_alphaShape and
> Pgr_pointsAsPolygon with the results of a pgr_dirvingDistance.
> All 3 functions are enabled when 'Driving Distance' is enabled so logical
> I assume that they are deisgned to be used together.
> I can take the results of a driving distance, which gives me a list of
> points, look up this list in by node table, which gives me a list of x/y
> values, I can then create a polygon from this list which will give me what
> I am after
> What will pgr_pointsAsPolygon/pgr_alphashape enabled me to do  in this
> context?


These features were not available in postgis in earlier version. 
Basically they were used to create concave polygons that represent the 
isochrones for the driving distance.

The code will get reviewed at the next major release and if it is 
obsoleted by the postgis code then we might consider removing them and 
just creating a wrapper that simplifies/automates creating the isochrones.


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