[pgrouting-users] Driving distance/pgr_alphaShape/pgr_pointsAsPolygon

Dave Potts dave.potts at pinan.co.uk
Tue Nov 11 13:56:11 PST 2014

On 11/11/14 18:00, Stephen Woodbridge wrote:
> 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?
> Dave,
> 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.
:-)  Thank you Steve, for clearing up that point.

> -Steve
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