How to find the distance between two points along a specific route?

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I'm developing an android app for my college that helps students track the current location of the college bus and also give them an estimated time when the bus might reach them. As of now I get the current location of the bus(via a device present on the bus) and the location of the student. I'm stuck at the point where I have to find the distance between the two GPS co-ordinates. I have to find the distance between the bus and the student "along a specific route" (i.e the path the bus takes). Using Google Map APIs will not always give the distance along the route I want. How do I find the distance between two points along a specific route?


I would it solve this way:

1) The direct line of sight distance betweent two GPS points is simple, simply use Location.distanceBetween() method, you will find hundres of posts here on SO.

2) The length of the route. This part is more difficult. If you are not happy with the result of google: Store your bus routes as rough sequence of lat/lon coordinates (a poly line). A point per street corner should be sufficient. Then find the nearest point on the route, a simple brute force search should be sufficent for your task. Then simply iterate from found route point till destination point, and sum up using the distanceBetween() method.