iPhone 3G: How to show locations around a fixed point?

Question

I have my current location fixed via CoreLocation. Now I want to get those locations (from an existing database), which are in the near (about 100 feet) of it.

How do I start?

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Update: Here is a implementation of the Haversine formula: http://www.jaimerios.com/?p=39 (very useful)

Answer 1

CLLocation provides a method for this:

- (CLLocationDistance)getDistanceFrom:(const CLLocation *)location

You'll need to have the latitude and longitude of each of your records, and then sort by the distance returned by this method.

Answer 2

High school geometry FTW:

dist = sqrt(pow((x2-x1), 2) + pow((y2-y1), 2))

One of the things you can do to make this easier to SQL Query, is to split the map into "tiles", i.e. a 2km x 2km area, so that you can query down to the tile, then loop through the results using this formula.