Moving from SQLite to Core Data - core-data

Question

I'm moving my SQLite database over to Core Data. My database table looks like this:
CREATE TABLE IF NOT EXISTS stops (id integer primary key autoincrement, type text, lat real, lon real, stop_id integer unique, stop_code integer, title text, subtitle text, url text, lastupdate text
My Entity looks like this:
I'm not worries about moving the data over, it's really just a local cache that gets updated from time to time. If its empty, it will just repopulate.
My issue is I have a SQLite custom function:
static void distanceFunc(sqlite3_context *context, int argc, sqlite3_value **argv)
{
// check that we have four arguments (lat1, lon1, lat2, lon2)
assert(argc == 4);
// check that all four arguments are non-null
if (sqlite3_value_type(argv[0]) == SQLITE_NULL || sqlite3_value_type(argv[1]) == SQLITE_NULL || sqlite3_value_type(argv[2]) == SQLITE_NULL || sqlite3_value_type(argv[3]) == SQLITE_NULL) {
sqlite3_result_null(context);
return;
}
// get the four argument values
double lat1 = sqlite3_value_double(argv[0]);
double lon1 = sqlite3_value_double(argv[1]);
double lat2 = sqlite3_value_double(argv[2]);
double lon2 = sqlite3_value_double(argv[3]);
// convert lat1 and lat2 into radians now, to avoid doing it twice below
double lat1rad = DEG2RAD(lat1);
double lat2rad = DEG2RAD(lat2);
// apply the spherical law of cosines to our latitudes and longitudes, and set the result appropriately
// 6378.1 is the approximate radius of the earth in kilometres
sqlite3_result_double(context, acos(sin(lat1rad) * sin(lat2rad) + cos(lat1rad) * cos(lat2rad) * cos(DEG2RAD(lon2) - DEG2RAD(lon1))) * 6378.1);
}
The function given a 2 latitudes and 2 longitudes would return the distance. This would let me do something like:
SELECT *, distance(lat, lon, %f, %f) as dist FROM stops WHERE dist < 1 ORDER BY dist
Now, I've got all my data in Core Data, but no idea how to do something like the SQL above with a NSFetchRequest. So how would I go about fetching entities in this manner?