Google/OR-Tools Get Duration And Distance - or-tools

Question

I'm trying to understand the solution call in the MVRP examples
I have two matrixes, duration and distance that have been returned via calls to google
My solution is based on distance but given that i have the data already returned i want to find the index associated with the duration.
unfortunately I'm not sure completely what is going on under the hood of the the Routing Calls so hoping for a simple fast answer for look up and what index to use
for simplicity sake I will show the google example rather than my code and highlight what im looking for:
public string PrintSolution()
{
// Inspect solution.
string ret = "";
long maxRouteDistance = 0;
for (int i = 0; i < _data.Drivers; ++i)
{
ret += $"Route for Vehicle {i}:";
ret += Environment.NewLine;
long routeDistance = 0;
var index = _routing.Start(i);
while (_routing.IsEnd(index) == false)
{
ret += $"{_manager.IndexToNode((int) index)} -> ";
var previousIndex = index;
index = _solution.Value(_routing.NextVar(index));
long legDistance = _routing.GetArcCostForVehicle(previousIndex, index, i);
//LOOKING FOR
//long legDuration = ??? what index am is using here to find in my duration matrix which is built the same as indexes as distance
ret += " leg distance: " + legDistance;
routeDistance += legDistance;
}
ret += $"{_manager.IndexToNode((int) index)}";
ret += Environment.NewLine;
ret += $"Distance of the route: {routeDistance}m";
ret += Environment.NewLine;
ret += Environment.NewLine;
maxRouteDistance = Math.Max(routeDistance, maxRouteDistance);
}
ret += $"Maximum distance of the routes: {maxRouteDistance}m";
ret += Environment.NewLine;
return ret;
}
#Mizux

Answer 1

disclaimer: This is a simplification but should help you to understand.
In OR-Tools Routing there is a primal "hidden" dimension without name but you can retrieve the cost using RoutingModel::GetArcCostForVehicle()
For any "regular" dimension you can get inspect the CumulVar at each node.
e.g. supposing you have created two dimensions using RoutingModel::AddDimension() whose name were "Distance" and "Duration".
note: CumulVar is an accumulator so if you want the "arc cost" you'll need something like this dim.CumulVar(next_index) - dim.CumulVar(index)
Then in you PrintFunction you can use:
public string PrintSolution()
{
...
RoutingDimension distanceDimension = routing.GetMutableDimension("Distance");
RoutingDimension durationDimension = routing.GetMutableDimension("Duration");
for (int i = 0; i < _manager.getNumberOfVehicles(); ++i)
{
while (_routing.IsEnd(index) == false)
{
...
IntVar distanceVar = distanceDimension.CumulVar(index);
IntVar durationVar = durationDimension.CumulVar(index);
long distance = _solution.Value(distanceVar);
long duration = _solution.Value(durationVar);
...
}
}
}