How to Efficiently Find the Nearest Locations in SQLite Without Custom Functions?

Getting the Nearest Locations in SQLite Using Haversine Formula

Storing latitude and longitude coordinates in your SQLite database opens up various possibilities for location-based applications. One common task is retrieving the nearest locations to a given point based on the Haversine formula. While MySQL natively supports this with custom functions, SQLite requires a more involved approach.

Custom External Functions for Haversine Formula

SQLite supports custom external functions for implementing advanced calculations. However, creating and integrating these functions can introduce unnecessary complexities and performance overhead. Additionally, sorting the results by distance requires adding a distance column to the database, which is both inefficient and impractical.

Efficient Filtering with Bounding Rectangle

A practical solution to this challenge involves filtering the database with a bounding rectangle. By calculating the four corners of the rectangle based on the given point and a predefined radius, you can eliminate most irrelevant data and significantly reduce the amount of processing required. The derived latitudes and longitudes can then be used to construct a WHERE clause for SQL queries:

PointF center = new PointF(x, y);
final double mult = 1.1; // Mult for more reliable results
PointF p1 = calculateDerivedPosition(center, mult * radius, 0);
PointF p2 = calculateDerivedPosition(center, mult * radius, 90);
PointF p3 = calculateDerivedPosition(center, mult * radius, 180);
PointF p4 = calculateDerivedPosition(center, mult * radius, 270);

strWhere =  " WHERE "
        + COL_X + " > " + String.valueOf(p3.x) + " AND "
        + COL_X + " < " + String.valueOf(p1.x) + " AND "
        + COL_Y + " < " + String.valueOf(p2.y) + " AND "
        + COL_Y + " > " + String.valueOf(p4.y);

Calculating Distance Within Filtered Results

Once the data is filtered, you can iterate through the results and calculate the actual distances using the Haversine formula:

public static boolean pointIsInCircle(PointF pointForCheck, PointF center,
            double radius) {
        if (getDistanceBetweenTwoPoints(pointForCheck, center) <= radius)
            return true;
        else
            return false;
    }

public static double getDistanceBetweenTwoPoints(PointF p1, PointF p2) {
        // Haversine formula for calculating distance in meters
        // ...
    }

By combining efficient filtering with accurate distance calculations, you can retrieve the nearest locations from your SQLite database without relying on custom external functions or persistent distance columns.

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