[pgrouting-users] Question about driving_distance calculation

[Markus Innerebner]

Daniel Kastl wrote:
>>
>>>  ok, thanks
>> The algorithm uses only the cost column(or reverse_cost column) of the
>> edges to compute the costs of the target vertex? This means there is no way
>> to compute the cost in dependency of a passed walking speed parameter, where
>> cost are defined as edge_length/speed.
>>
>>
> The cost is what you define as cost. Anything is OK. You select the cost
> column in your query, which can be a combination of several attributes.
ok, perfect.

My last question now:
the function returns a edge_id, described by the identifier of the edge 
crossed. What is the benefit of this attribute? What does this edge do?
If the result contains the vertices reached in the given time from the 
query point, why also adding the edge identifier?

Markus