Android: How to detect if users if within distance of GeoPoint on MapVIew

I have an application with a map and an ItemizedOverlay, and need to determine if t开发者_JS百科he user is within a certain distance of a GeoPoint on the ItemizedOverlay. If thats the case then start a new Activity..

How do I approach this?

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It sounds like you have various things you need to do, I would break it down into the following

1. Obtain the users GeoPoint, have a look at this API it might be useful
2. Determine the distance between the users GeoPoint and any other given GeoPoint, I found this article which explains how to calculate distances, its worth a read
3. If the distance meets a particular requirement, then start a new activity, for this I would suggest to read up on Intents/Lifecycle. You could create a new intent and use startActivity(intent); which would start another activity, you can read more here