# Reverse driving distance

I am used to using pgr-route driving distance function to calculate how far I can go from a given point to a surrounding area

Assuming that I have a transport graph that includes costs and reverse costs is there any way off generating how long it takes to reach a single point from the surrounding area ? A reverse driving distance ?

The only way I can think of doing this is to calculating the driving time for a series of points around the central point, but that strikes me as a rather expensive way of doing it.

Note my data includes cost and reverse costs values so I can just invert a driving distance calculation.

• What would be a real-world use case for this? You write "how long it takes to reach a single point from the surrounding area", but then you just look at a single point and you can use driving distance function from that point. – dkastl Dec 27 '18 at 20:32
• I am dealing with a shipping network, dealing with networks flows, the driving distance calculation give me a time for a point to supply the network, I am trying to looking in to the issue of time to supply the point. One of my problems is that I do not known how much the network is supplying, so the point that can accept the maximum is an important issue to consider. – Dave Dec 28 '18 at 6:22

## 1 Answer

Since you have to supply pg_routing with the `target`, `source`, `cost` and `reverse_cost` fields anyway, this is quite simple: Just switch the fields/values you give it for `cost` and `reverse_cost`. Unless I'm mistaken, this should let you estimate network costs 'backwards' from the point of interest.