What's the Most Accurate Way to Calculate Distance Between Geographic Coordinates Using SQL Server?

Precise Geographic Distance Calculation in SQL Server: Haversine vs. Geography Type

Accurately calculating distances between geographic coordinates is crucial for many applications, including navigation and location-based services. This article compares two methods for achieving this in SQL Server: using the Haversine formula and utilizing the built-in geography data type.

The Haversine formula, while commonly used, can suffer from inaccuracies due to limitations in floating-point precision. Previous attempts using this formula may have yielded less-than-ideal results.

SQL Server 2008 introduced the geography data type, offering a superior solution for handling geographic data. Its key advantages include:

• Enhanced Precision: Coordinates are stored as doubles, minimizing precision errors.
• Simplified Calculations: The STDistance method directly computes distances, eliminating the need for manual Haversine formula implementation.
• Expanded Functionality: The geography type provides a rich set of geospatial functions beyond distance calculation.

Illustrative Query using Geography Type

The following SQL query demonstrates distance calculation using the geography type:

DECLARE @source geography = geography::Point(0, 51.5);
DECLARE @target geography = geography::Point(-3, 56);

SELECT @source.STDistance(@target);

This returns the distance in meters.

Conclusion: Choosing the Right Approach

For optimal accuracy and ease of use, the geography data type in SQL Server 2008 and later versions is the recommended method for calculating distances between geographic coordinates. While the Haversine formula can be employed, careful consideration of data types and potential precision issues is necessary. The geography type offers a more robust and efficient solution for most applications.

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