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Needing some direction on where to start

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I am aware of how to calculate mileage or distance by way of the "great circle" calculation but I'm really wanting to take this a step further and do so via map data.


I'm not interested at this time in displaying or showing maps, etc. although I may get to that later. All I want right now is to be able to enter a starting and ending point say zipcode and get a fairly accurate (+/- 10%) mileage calculation based on roads, my problem is I have no idea where to start.


I have downloaded the navteq transportation sample data but its pretty greek at this point so any helpful pointers or direction would be appreciative.



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Fran├žois Goulet

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I don't know the format of the Navteq transportation sample data, but QGIS with the Road graph plugin should be a good place to start...


Calculating shortest path in QGIS using Road graph




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I also don't know what NavTeq data is like, but typically GPS-intended data like that already has distances for each road segment. I think those distances are recorded from actual travelling, though I'm not certain of that; they could theoretically also be computed from the data themselves, in which case they were either done in an appropriate map projection (decent), by Great Circle calcuations (best), or in an inappropriate map projection (possible significant errors).


Anyway, if those distances are there, then the distance of a routing is simply a sum of segment distances.


The most error-free thing you could do would be to calculate the Great Circle distance of every line segment between two vertices along a route, though this might be computationally expensive if your network is really big. Could do that for each segment ahead of time, and store that summed distance as an attribute of each segment (i.e., calculating them as mentioned above), thereby allowing you to simply sum on demand.




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