[pgrouting-users] polygons of drivingDistance

[Jakob Miksch]

Dear List,

I calculated the pgr_DrivingDistance for two costs (10 min, 20min). Then 
I used pgr_pointsAsPolygon  in order to get polygons out of my points. 
Usually it works well, but sometimes the polygon with the "lower" cost 
covers some areas which the polygon with "higher" cost does NOT cover. 
Here is an example:

https://www.dropbox.com/s/tblyp7q4sp56sla/Error%20Alphashape.png?dl=0
(green=low cost   red=high cost)

My goal is that polygons with "lower" cost are completely inside 
polygons with "higher" cost.

How would you approach this issue?

Best,
Jakob