Android算法用于查找给定距离内的所有Geopoints

Question

In my naive beginning Android mind I thought the way to do this would be to loop through each of the objects checking if proximity falls within X range and if so, include the object. This is being done with Google Maps and GeoPoints.

That said, I know this is probably the slowest way possibly. I did a search for Android Proxmity algorithm's and did not get much really. What I am looking for is best options with regard to this the more efficiently.

Are there any libraries I have not been able to find?

If not, should I load these Location objects into SQL then go from there or keep them in a JSONArray?

Once I establish my best datastructure, what is he best method to find all Locations located with X miles of user?

I am not asking for cut and paste code, rather the best method to this efficiently. Then, I can stumble through the code :)

My first gut feeling is to group the Locations by regions but I'm not exactly sure how to do this.

I could potentially have tens of thousands of datapoints.

Any help in simply heading in the right direction is greatly appreciated.

As a side note, I reach this juncture after discovering that a remote API I had been using was.. well.. just PLAIN WRONG and ommiting datapoints from my proximity search. I also realized that if just placed on the datapoints on the phone, then I could allow the user to run the App without internet connection, and only GPS and this would be a HUGE plus. So, with all setbacks come opportunnities!

Answer 1

The answer depends on the representation of the GeoPoints: If these are not sorted you need to scan all of them (this is done in linear time, sorting wrt. distance or clustering will be more expensive). Use Location.distanceTo(Location) or Location.distanceBetween(float, float, float, float, float[]) to calculate the distances.

If the GeoPoints were sorted wrt. distance to your position this task can be done much more efficiently, but since the supplier does not know your position, I assume that this cannot be done.

If the GeoPoints are clustered, ie if you have a set of clusters with some center and a radius select each cluster where the distance from your position to the cluster's center is within the limit plus the radius. For these clusters you need to check each GeoPoint contained in the cluster (some of them are possibly farther away from your position than the limit allows). Alternatively you might accept the error and include all points of the cluster (if the radius is relatively small I would recommend this).