Calculation route length

Question

Hi,

I have a map with about 80 annotations. I would like to do 3 things.

1) From my current location, I would like to know the actual route distance to that position. Not the linear distance.

2) I want to be able to show a list of all the annotations, but for every annotation (having lon/lat) I would like to know the actual route distance from my position to that position.

3) I would like to know the closest annotation to my possition using route distance. Not linear distance.

I think the answer to all these three points will be the same. But please keep in mind that I don't want to create a route, I just want to know the distance to the annotation.

I hope someone can help me.

Best regards, Paul Peelen

Answer 1

Calculating route distance to about 80 locations is certain to be computationally intensive on Google's part and I can't imagine that you would be able to make those requests to the Google Maps API, were it possible to do so on a mobile device, without being severely limited by either the phone connection or rate limits on the server.

Unfortunately, calculating route distance rather than geometric distance is a very expensive computation involving a lot of data about the area - data you almost certainly don't have. This means, unfortunately, that this isn't something that Core Location or MapKit can help you with.

What problem are you trying to solve, exactly? There may be other heuristics other than route distance you can use to approximate some sort of distance ranking.

Answer 2

Hello, I think as pointed out before, your query would be extremely heavy for google maps API if you perform exactly what you are saying. Do you need all that information at once ? Maybe first it would be good enough to query just some of the distances based on some heuristic or in the user needs.

To obtain the distances, you could use a Google Maps GDirections object... as pointed out here ( at the bottom of the page there's "Routes and Steps" section, with an advanced example.

"The GDirections object also supports multi-point directions, which can be constructed using the GDirections.loadFromWaypoints() method. This method takes an array of textual input addresses or textual lat/lon points. Each separate waypoint is computed as a separate route and returned in a separate GRoute object, each of which contains a series of GStep objects."

Using the Google Maps API in the iPhone shouldn't be too difficult, and I think your question doesn't cover that, but if you need some basic example, you could look at this question, and scroll to the answer.

Good Luck!

Answer 3

From what I understand of your post, I believe you seek the Haversine formula. Luckily for you, there are a number of Objective-C implementations, though writing your own is trivial once the formula's in front of you.

I originally deleted this because I didn't notice that you didn't want linear distance at first, but I'm bringing it back in case you decide that an approximation is good enough at that particular point of the user interaction.