Distance Calculation using Haversine

Code Explanation

The provided code calculates the distance between two points on the Earth's surface using latitude and longitude coordinates.

1. It starts by declaring and initializing variables to store the latitude and longitude values of the two points:

• lat1 is assigned the value of the latitude of the first point from the 'Table' column 'Latitude1' in radians.
• lon1 is assigned the value of the longitude of the first point from the 'Table' column 'Longitude1' in radians.
• lat2 is assigned the value of the latitude of the second point from the 'Table' column 'Latitude2' in radians.
• lon2 is assigned the value of the longitude of the second point from the 'Table' column 'Longitude2' in radians.

2. The code then calculates the differences in latitude and longitude:

• dlat represents the difference in latitude between the two points (lat2 - lat1).
• dlon represents the difference in longitude between the two points (lon2 - lon1).

3. The code proceeds to calculate the distance between the two points using the Haversine formula, which is based on trigonometry.

• The formula calculates the "great circle distance" between two points on a sphere (in this case, the Earth).
• a is calculated as the sum of the following terms:
  • The square of the sine of half the latitude difference (SIN(dlat/2) * SIN(dlat/2)).
  • The product of the cosine of the first latitude, the cosine of the second latitude, and the square of the sine of half the longitude difference (COS(lat1) * COS(lat2) * SIN(dlon/2) * SIN(dlon/2)).
• c is calculated as the arctangent of the square root of a divided by the square root of (1 - a) (2 * ATAN2(SQRT(a), SQRT(1-a))).
• Finally, the distance variable is calculated as the product of c and the Earth's radius in kilometers (6371).

4. The calculated distance, stored in the distance variable, is then returned as the output of the calculation.

Key Concepts

• RADIANS function is used to convert degrees to radians, which is a widely used unit of measurement in trigonometry calculations.
• Haversine formula is used to calculate the distance between two points on a sphere, such as the Earth's surface.
• The formula takes into account the curvature of the Earth, making it more accurate for long distances compared to other distance calculation methods.

Additional Example

Here's an example of how the code can be used in practice:

Distance = 
VAR lat1 = RADIANS(37.7749) -- Latitude of point 1 in degrees
VAR lon1 = RADIANS(-122.4194) -- Longitude of point 1 in degrees
VAR lat2 = RADIANS(34.0522) -- Latitude of point 2 in degrees
VAR lon2 = RADIANS(-118.2437) -- Longitude of point 2 in degrees
VAR dlat = lat2 - lat1
VAR dlon = lon2 - lon1
VAR a =
    SIN(dlat/2) * SIN(dlat/2) +
    COS(lat1) * COS(lat2) *
    SIN(dlon/2) * SIN(dlon/2)
VAR c = 2 * ATAN2(SQRT(a), SQRT(1-a))
VAR distance = c * 6371 -- Earth radius in kilometers

RETURN distance

This example calculates the distance between San Francisco (latitude 37.7749, longitude -122.4194) and Los Angeles (latitude 34.0522, longitude -118.2437) and returns the result. The output would be the approximate distance between the two cities in kilometers.