hi,
Ideally they should not differ. And yes, snapping distances are not added (as far as I am sure). Do you have problems with all the pairs ? If not, just have another look at your cutoff distance parameter in your settings for OD matrix. This should not be the reason, but just have a look. .
As the documentation suggests, OD matrix is a quick solver and does not take into account shapes. May be there are slight differences in the manual version and OD (batch) versions of the algorithms. I stand under correction.
The OD and all Network Analyst solvers find paths from the location where they snapped on the network. If your point is 30 meters away and you solve on travel time, how do you add the 30 meters to the travel time. So the total path length (in attribute units) is always on the network. It has nothing to do with the CUTOFF which is used to limit how far away you want to compute the distances too.
Where does the documentation suggest that OD does not take into account shapes? The OD solver and all the Network Analyst solvers compute distances on the actual network. The only thing OD does not return back (for performance reason) is the actual geometry of the path taken. The OD is used when all you want is the network distance and do not care to see the path geometry.
So to answer the original post, OD returns back distances on the network. If you want to add the snapping distance, then first use the GP tool Calculate Locations on your points. This will add the network location fields and also the x,y of the snapped point and distance to the network edge (make sure your projection is set to return the same distance unit as what you are solving on so that you get miles from edge if you are solving to minimize miles or you can convert it later with field calulator). Now create the OD layer and when you do load location, use the network location fields AND map the distance to the Attr_Length (or what ever the name of your distance attribute is). Now when you solve, the distance to the network will be added to the path length returned back after the solve.
Jay Sandhu
hi,
Ideally they should not differ. And yes, snapping distances are not added (as far as I am sure). Do you have problems with all the pairs ? If not, just have another look at your cutoff distance parameter in your settings for OD matrix. This should not be the reason, but just have a look.
As the documentation suggests, OD matrix is a quick solver and does not take into account shapes. May be there are slight differences in the manual version and OD (batch) versions of the algorithms. I stand under correction.
Probably you should quantify your differences. Are they always differ by same amount, same percentage, may be some peculiar network edge common to all your (error) paths.
In that case I will suggest that you use the Closest Facility solver instead of the OD. Use the Origins as Incidents and the Destinations will be Facilities and make sure on the Analysis Settings to set the Facilities to Find to the total number of destinations you have. You should be able to map the "distance" to the Attr_Length on both facilities and destinations.
Jay Sandhu